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  • 151. Abdo, A.A.
    et al.
    Jackson, Miranda
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et al.,
    Fermi-lat discovery of gev gamma-ray emission from the young supernova remnant cassiopeia A2010Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 710, nr 1, s. L92-L97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the first detection of GeV high-energy gamma-ray emission from a young supernova remnant (SNR) with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope. These observations reveal a source with no discernible spatial extension detected at a significance level of 12.2 sigma above 500 MeV a a location that is consistent with the position of the remnant of the supernova explosion that occurred around 1680 in the Cassiopeia constellation-Cassiopeia A (Cas A). The gamma-ray flux and spectral shape of the source are consistent with a scenario in which the gamma-ray emission originates from relativistic particles accelerated in the shell of this remnant. The total content of cosmic rays (electrons and protons) accelerated in Cas A can be estimated as W(CR) similar or equal to (1-4) x 10(49) erg thanks to the well-known density in the remnant assuming that the observed gamma ray originates in the SNR shell(s). The magnetic field in the radio-emitting plasma can be robustly constrained as B >= 0.1 mG, providing new evidence of the magnetic field amplification at the forward shock and the strong field in the shocked ejecta.

  • 152. Abdo, A.A
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M
    et al, et al
    DETECTION OF GAMMA-RAY EMISSION FROM THE STARBURST GALAXIES M82 AND NGC 253 WITH THE LARGE AREA TELESCOPE ON FERMI2010Ingår i: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8213, Vol. 709, nr 2, s. L152-L157Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been detected at significance levels of 6.8 sigma and 4.8 sigma, respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with gamma-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and gamma-ray emission in star-forming galaxies.

  • 153. Abdo, A.A
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M
    et al, et al
    SPECTRAL PROPERTIES OF BRIGHT FERMI-DETECTED BLAZARS IN THE GAMMA-RAY BAND2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 710, nr 2, s. 1271-1285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The gamma-ray energy spectra of bright blazars of the LAT Bright AGN Sample LBAS) are investigated using Fermi-LAT data. Spectral properties hardness, curvature, and variability) established using a data set accumulated over 6 months of operation are presented and discussed for different blazar classes and subclasses: flat spectrum radio quasars (FSRQs), low-synchrotron peaked BLLacs (LSP-BLLacs), intermediate-synchrotron peaked BLLacs (ISP-BLLacs), and high-synchrotron peaked BLLacs (HSP-BLLacs). The distribution of photon index G, obtained from a power-law fit above 100 MeV) is found to correlate strongly with blazar subclass. The change in spectral index from that averaged over the 6 months observing period is < 0.2-0.3 when the flux varies by about an order of magnitude, with a tendency toward harder spectra when the flux is brighter for FSRQs and LSP-BLLacs. A strong departure from a single power-law spectrum appears to be a common feature for FSRQs. This feature is also present for some high-luminosity LSP-BLLacs, and a small number of ISP-BLLacs. It is absent in all LBAS HSP-BLLacs. For 3C 454.3 and AO 0235+164, the two brightest FSRQ source and LSP-BLLac source, respectively, a broken power law (BPL) gives the most acceptable of power law, BPL, and curved forms. The consequences of these findings are discussed.

  • 154.
    Abdollahi, S.
    et al.
    Univ Toulouse, UPS, CNRS, CNES,IRAP, F-31028 Toulouse, France..
    Ballet, J.
    Univ Paris Saclay, F-91191 Gif Sur Yvette, France.;Univ Paris Cite, CEA, CNRS, AIM, F-91191 Gif Sur Yvette, France..
    Johannesson, G.
    Nordita SU; Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;Dalarna Univ, Sch Educ Hlth & Social Studies, Nat Sci, SE-79188 Falun, Sweden..
    Zaharijas, G.
    Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    Search for New Cosmic-Ray Acceleration Sites within the 4FGL Catalog Galactic Plane Sources2022Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 933, nr 2, artikel-id 204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cosmic rays are mostly composed of protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma-rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum, with a low-energy break around 200 MeV, was detected in the gamma-ray spectra of four supernova remnants (SNRs), IC 443, W44, W49B, and W51C, with the Fermi Large Area Telescope. This detection provided direct evidence that cosmic-ray protons are (re-)accelerated in SNRs. Here, we present a comprehensive search for low-energy spectral breaks among 311 4FGL catalog sources located within 5 degrees from the Galactic plane. Using 8 yr of data from the Fermi Large Area Telescope between 50 MeV and 1 GeV, we find and present the spectral characteristics of 56 sources with a spectral break confirmed by a thorough study of systematic uncertainty. Our population of sources includes 13 SNRs for which the proton-proton interaction is enhanced by the dense target material; the high-mass gamma-ray binary LS I+61 303; the colliding wind binary eta Carinae; and the Cygnus star-forming region. This analysis better constrains the origin of the gamma-ray emission and enlarges our view to potential new cosmic-ray acceleration sites.

  • 155.
    Abdollahi, S.
    et al.
    Univ Toulouse, IRAP, CNRS, UPS,CNES, F-31028 Toulouse, France.;Stanford Univ, Dept Phys, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Ballet, J.
    Univ Paris Saclay, F-91191 Gif Sur Yvette, France.;Univ Paris Cite, CEA, CNRS, AIM, F-91191 Gif Sur Yvette, France..
    Jóhannesson, Guðlaugur
    Univ Iceland, Inst Sci, IS-107 Reykjavik, Iceland.;Nordita, SU.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;Dalarna Univ, Sch Educ Hlth & Social Studies, Nat Sci, SE-79188 Falun, Sweden..
    Zaharijas, G.
    Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    Incremental Fermi Large Area Telescope Fourth Source Catalog2022Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 260, nr 2, s. 53-, artikel-id 53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi Large Area Telescope (LAT) catalog of gamma-ray sources. Based on the first 12 years of science data in the energy range from 50 MeV to 1 TeV, it contains 6658 sources. The analysis improves on that used for the 4FGL catalog over eight years of data: more sources are fit with curved spectra, we introduce a more robust spectral parameterization for pulsars, and we extend the spectral points to 1 TeV. The spectral parameters, spectral energy distributions, and associations are updated for all sources. Light curves are rebuilt for all sources with 1 yr intervals (not 2 month intervals). Among the 5064 original 4FGL sources, 16 were deleted, 112 are formally below the detection threshold over 12 yr (but are kept in the list), while 74 are newly associated, 10 have an improved association, and seven associations were withdrawn. Pulsars are split explicitly between young and millisecond pulsars. Pulsars and binaries newly detected in LAT sources, as well as more than 100 newly classified blazars, are reported. We add three extended sources and 1607 new point sources, mostly just above the detection threshold, among which eight are considered identified, and 699 have a plausible counterpart at other wavelengths. We discuss the degree-scale residuals to the global sky model and clusters of soft unassociated point sources close to the Galactic plane, which are possibly related to limitations of the interstellar emission model and missing extended sources.

  • 156.
    Abe, K.
    et al.
    Univ Tokyo, Inst Cosm Ray Res, Kamioka Observ, Kamioka, Akita, Japan.;Univ Tokyo, Univ Tokyo Inst Adv Study, Kavli Inst Phys & Math Universe WPI, Kashiwa, Chiba, Japan.;Univ Tokyo, Next Generat Neutrino Sci Org, Kamioka, Akita, Japan..
    Choubey, Sandhya
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Teoretisk partikelfysik.
    Zsoldos, S.
    Kings Coll London, Dept Phys, Strand Bldg, London, England..
    Supernova Model Discrimination with Hyper-Kamiokande2021Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 916, nr 1, artikel-id 15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants-neutron stars and black holes-are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokande's response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations toward a precise reproduction of the explosion mechanism observed in nature.

  • 157.
    Abolmasov, Pavel
    et al.
    Univ Turku, Dept Phys & Astron, Turku 20014, Finland.;Moscow MV Lomonosov State Univ, Sternberg Astron Inst, Univ Sky Pr 13, Moscow 119234, Russia..
    Nättilä, Joonas
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Columbia Univ, Phys Dept, 538 West 120th St, New York, NY 10027 USA.;Columbia Univ, Columbia Astrophys Lab, 538 West 120th St, New York, NY 10027 USA.;Flatiron Inst, Ctr Computat Astrophys, 162 Fifth Ave, New York, NY 10010 USA.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Poutanen, Juri
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Univ Turku, Dept Phys & Astron, Turku 20014, Finland.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Russian Acad Sci, Space Res Inst, Profsoyuznaya Str 84-32, Moscow 117997, Russia..
    Kilohertz quasi-periodic oscillations from neutron star spreading layers2020Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 638, s. A142-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When the accretion disc around a weakly magnetised neutron star (NS) meets the stellar surface, it should brake down to match the rotation of the NS, forming a boundary layer. As the mechanisms potentially responsible for this braking are apparently inefficient, it is reasonable to consider this layer as a spreading layer (SL) with negligible radial extent and structure. We perform hydrodynamical 2D spectral simulations of an SL, considering the disc as a source of matter and angular momentum. Interaction of new, rapidly rotating matter with the pre-existing, relatively slow material co-rotating with the star leads to instabilities capable of transferring angular momentum and creating variability on dynamical timescales. For small accretion rates, we find that the SL is unstable for heating instability that disrupts the initial latitudinal symmetry and produces large deviations between the two hemispheres. This instability also results in breaking of the axial symmetry as coherent flow structures are formed and escape from the SL intermittently. At enhanced accretion rates, the SL is prone to shearing instability and acts as a source of oblique waves that propagate towards the poles, leading to patterns that again break the axial symmetry. We compute artificial light curves of an SL viewed at different inclination angles. Most of the simulated light curves show oscillations at frequencies close to 1 kHz. We interpret these oscillations as inertial modes excited by shear instabilities near the boundary of the SL. Their frequencies, dependence on flux, and amplitude variations can explain the high-frequency pair quasi-periodic oscillations observed in many low-mass X-ray binaries.

  • 158. Abramowski, A.
    et al.
    Acero, F.
    Aharonian, F.
    Akhperjanian, A. G.
    Anton, G.
    Balzer, A.
    Barnacka, A.
    de Almeida, U. Barres
    Becherini, Y.
    Becker, J.
    Behera, B.
    Bernloehr, K.
    Birsin, E.
    Biteau, J.
    Bochow, A.
    Boisson, C.
    Bolmont, J.
    Bordas, P.
    Brucker, J.
    Brun, F.
    Brun, P.
    Bulik, T.
    Bueching, I.
    Carrigan, S.
    Casanova, S.
    Cerruti, M.
    Chadwick, P. M.
    Charbonnier, A.
    Chaves, R. C. G.
    Cheesebrough, A.
    Clapson, A. C.
    Coignet, G.
    Cologna, G.
    Conrad, Jan
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Dalton, M.
    Daniel, M. K.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    Dickinson, Hugh J.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Djannati-Atai, A.
    Domainko, W.
    Drury, L. O 'C.
    Dubus, G.
    Dutson, K.
    Dyks, J.
    Dyrda, M.
    Egberts, K.
    Eger, P.
    Espigat, P.
    Fallon, L.
    Farnier, C.
    Fegan, S.
    Feinstein, F.
    Fernandes, M. V.
    Fiasson, A.
    Fontaine, G.
    Foerster, A.
    Fuessling, M.
    Gallant, Y. A.
    Gast, H.
    Gerard, L.
    Gerbig, D.
    Giebels, B.
    Glicenstein, J. F.
    Glueck, B.
    Goret, P.
    Goering, D.
    Haeffner, S.
    Hague, J. D.
    Hampf, D.
    Hauser, M.
    Heinz, S.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hinton, J. A.
    Hoffmann, A.
    Hofmann, W.
    Hofverberg, P.
    Holler, M.
    Horns, D.
    Jacholkowska, A.
    de Jager, O. C.
    Jahn, C.
    Jamrozy, M.
    Jung, I.
    Kastendieck, M. A.
    Katarzynski, K.
    Katz, U.
    Kaufmann, S.
    Keogh, D.
    Khangulyan, D.
    Khelifi, B.
    Klochkov, D.
    Kluzniak, W.
    Kneiske, T.
    Komin, Nu
    Kosack, K.
    Kossakowski, R.
    Laffon, H.
    Lamanna, G.
    Lennarz, D.
    Lohse, T.
    Lopatin, A.
    Lu, C. -C
    Marandon, V.
    Marcowith, A.
    Masbou, J.
    Maurin, D.
    Maxted, N.
    Mayer, M.
    McComb, T. J. L.
    Medina, M. C.
    Mehault, J.
    Moderski, R.
    Moulin, E.
    Naumann, C. L.
    Naumann-Godo, M.
    de Naurois, M.
    Nedbal, D.
    Nekrassov, D.
    Nguyen, N.
    Nicholas, B.
    Niemiec, J.
    Nolan, S. J.
    Ohm, S.
    Wilhelmi, E. de Ona
    Opitz, B.
    Ostrowski, M.
    Oya, I.
    Panter, M.
    Arribas, M. Paz
    Pedaletti, G.
    Pelletier, G.
    Petrucci, P. -O
    Pita, S.
    Puehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raue, M.
    Rayner, S. M.
    Reimer, A.
    Reimer, O.
    Renaud, M.
    de los Reyes, R.
    Rieger, F.
    Ripken, Joachim
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rob, L.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Ruppel, J.
    Sahakian, V.
    Sanchez, D. A.
    Santangelo, A.
    Schlickeiser, R.
    Schoeck, F. M.
    Schulz, A.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Sheidaei, F.
    Skilton, J. L.
    Sol, H.
    Spengler, G.
    Stawarz, L.
    Steenkamp, R.
    Stegmann, C.
    Stinzing, F.
    Stycz, K.
    Sushch, I.
    Szostek, A.
    Tavernet, J. -P
    Terrier, R.
    Tluczykont, M.
    Valerius, K.
    van Eldik, C.
    Vasileiadis, G.
    Venter, C.
    Vialle, J. P.
    Viana, A.
    Vincent, P.
    Voelk, H. J.
    Volpe, F.
    Vorobiov, S.
    Vorster, M.
    Wagner, S. J.
    Ward, M.
    White, R.
    Wierzcholska, A.
    Zacharias, M.
    Zajczyk, A.
    Zdziarski, A. A.
    Zech, A.
    Zechlin, H. -S
    Search for dark matter annihilation signals from the Fornax galaxy cluster with H.E.S.S.2012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 750, nr 2, s. 123-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Fornax galaxy cluster was observed with the High Energy Stereoscopic System for a total live time of 14.5 hr, searching for very high energy (VHE; E > 100GeV) gamma-rays from dark matter (DM) annihilation. No significant signal was found in searches for point-like and extended emissions. Using several models of the DM density distribution, upper limits on the DM velocity-weighted annihilation cross-section <sigma upsilon > as a function of the DM particle mass are derived. Constraints are derived for different DM particle models, such as those arising from Kaluza-Klein and supersymmetric models. Various annihilation final states are considered. Possible enhancements of the DM annihilation gamma-ray flux, due to DM substructures of the DM host halo, or from the Sommerfeld effect, are studied. Additional gamma-ray contributions from internal bremsstrahlung and inverse Compton radiation are also discussed. For a DM particle mass of 1 TeV, the exclusion limits at 95% of confidence level reach values of <sigma upsilon >(95% C.L.) similar to 10(-23) cm(3) s(-1), depending on the DM particle model and halo properties. Additional contribution from DM substructures can improve the upper limits on <sigma upsilon > by more than two orders of magnitude. At masses around 4.5 TeV, the enhancement by substructures and the Sommerfeld resonance effect results in a velocity-weighted annihilation cross-section upper limit at the level of <sigma upsilon >(95% C.L.) similar to 10(-26) cm(3) s(-1).

  • 159. Abramowski, A.
    et al.
    Acero, F.
    Aharonian, F.
    Akhperjanian, A. G.
    Anton, G.
    de Almeida, U. Barres
    Bazer-Bachi, A. R.
    Becherini, Y.
    Behera, B.
    Benbow, W.
    Bernloehr, K.
    Bochow, A.
    Boisson, C.
    Bolmont, J.
    Borrel, V.
    Brucker, J.
    Brun, F.
    Brun, P.
    Buehler, R.
    Bulik, T.
    Buesching, I.
    Boutelier, T.
    Chadwick, P. M.
    Charbonnier, A.
    Chaves, R. C. G.
    Cheesebrough, A.
    Conrad, J.
    Chounet, L. -M
    Clapson, A. C.
    Coignet, G.
    Costamante, L.
    Dalton, M.
    Daniel, M. K.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    Dickinson, H. J.
    Djannati-Atai, A.
    Domainko, W.
    Drury, L. O 'C.
    Dubois, F.
    Dubus, G.
    Dyks, J.
    Dyrda, M.
    Egberts, K.
    Eger, P.
    Espigat, P.
    Fallon, L.
    Farnier, C.
    Fegan, S.
    Feinstein, F.
    Fernandes, M. V.
    Fiasson, A.
    Foerster, A.
    Fontaine, G.
    Fuessling, M.
    Gabici, S.
    Gallant, Y. A.
    Gerard, L.
    Gerbig, D.
    Giebels, B.
    Glicenstein, J. F.
    Glueck, B.
    Goret, P.
    Goering, D.
    Hampf, D.
    Hauser, M.
    Heinz, S.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hinton, J. A.
    Hoffmann, A.
    Hofmann, W.
    Hofverberg, P.
    Holleran, M.
    Hoppe, S.
    Horns, D.
    Jacholkowska, A.
    de Jager, O. C.
    Jahn, C.
    Jung, I.
    Katarzynski, K.
    Katz, U.
    Kaufmann, S.
    Kerschhaggl, M.
    Khangulyan, D.
    Khelifi, B.
    Keogh, D.
    Klochkov, D.
    Kluzniak, W.
    Kneiske, T.
    Komin, Nu.
    Kosack, K.
    Kossakowski, R.
    Lamanna, G.
    Lenain, J. -P
    Lohse, T.
    Lu, C. -C
    Marandon, V.
    Marcowith, A.
    Masbou, J.
    Maurin, D.
    McComb, T. J. L.
    Medina, M. C.
    Mehault, J.
    Moderski, R.
    Moulin, E.
    Naumann-Godo, M.
    de Naurois, M.
    Nedbal, D.
    Nekrassov, D.
    Nguyen, N.
    Nicholas, B.
    Niemiec, J.
    Nolan, S. J.
    Ohm, S.
    Olive, J. -F
    Wilhelmi, E. de Ona
    Opitz, B.
    Orford, K. J.
    Ostrowski, M.
    Panter, M.
    Arribas, M. Paz
    Pedaletti, G.
    Pelletier, G.
    Petrucci, P. -O
    Pita, S.
    Puehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raubenheimer, B. C.
    Raue, M.
    Rayner, S. M.
    Reimer, O.
    Renaud, M.
    de los Reyes, R.
    Rieger, F.
    Ripken, J.
    Rob, L.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Ruppel, J.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sahakian, V.
    Santangelo, A.
    Schlickeiser, R.
    Schoeck, F. M.
    Schoenwald, A.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Shalchi, A.
    Sushch, I.
    Sikora, M.
    Skilton, J. L.
    Sol, H.
    Stawarz, L.
    Steenkamp, R.
    Stegmann, C.
    Stinzing, F.
    Szostek, A.
    Tam, P. H.
    Tavernet, J. -P
    Terrier, R.
    Tibolla, O.
    Tluczykont, M.
    Valerius, K.
    van Eldik, C.
    Vasileiadis, G.
    Venter, C.
    Venter, L.
    Vialle, J. P.
    Viana, A.
    Vincent, P.
    Vivier, M.
    Voelk, H. J.
    Volpe, F.
    Vorobiov, S.
    Wagner, S. J.
    Ward, M.
    Zdziarski, A. A.
    Zech, A.
    Zechlin, H. -S
    Multi-wavelength observations of H 2356-3092010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 516, s. A56-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. The properties of the broad-band emission from the high-frequency peaked BL Lac H 2356-309 (z = 0.165) are investigated. Methods. Very high energy (VHE; E > 100 GeV) observations of H 2356-309 were performed with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Simultaneous optical/UV and X-ray observations were made with the XMM-Newton satellite on June 12/13 and June 14/15, 2005. NRT radio observations were also contemporaneously performed in 2005. ATOM optical monitoring observations were also made in 2007. Results. A strong VHE signal, similar to 13 sigma total, was detected by HESS after the four years HESS observations (116.8 h live time). The integral flux above 240 GeV is I(> 240 GeV) = (3.06 +/- 0.26(stat) +/- 0.61(syst)) x 10(-12) cm(-2) s(-1), corresponding to similar to 1.6% of the flux observed from the Crab Nebula. A time-averaged energy spectrum is measured from 200 GeV to 2 TeV and is characterized by a power law (photon index of Gamma = 3.06 +/- 0.15(stat) +/- 0.10(syst)). Significant small-amplitude variations in the VHE flux from H 2356-309 are seen on time scales of months and years, but not on shorter time scales. No evidence for any variations in the VHE spectral slope are found within these data. The XMM-Newton X-ray measurements show a historically low X-ray state, characterized by a hard, broken-power-law spectrum on both nights. Conclusions. The broad-band spectral energy distribution (SED) of the blazar can be adequately fit using a simple one-zone synchrotron self-Compton (SSC) model. In the SSC scenario, higher VHE fluxes could be expected in the future since the observed X-ray flux is at a historically low level.

  • 160. Abramowski, A.
    et al.
    Acero, F.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zechlin, H. -S
    Dubner, G.
    Detection of very-high-energy gamma-ray emission from the vicinity of PSR B1706-44 and G 343.1-2.3 with HESS2011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 528, s. A143-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The gamma-ray pulsar PSR B1706-44 and the adjacent supernova remnant (SNR) candidate G 343.1-2.3 were observed by H. E. S. S. during a dedicated observation campaign in 2007. As a result of this observation campaign, a new source of very-high-energy (VHE; E > 100 GeV) gamma-ray emission, H.E.S.S. J1708-443, was detected with a statistical significance of 7 sigma, although no significant point-like emission was detected at the position of the energetic pulsar itself. In this paper, the morphological and spectral analyses of the newly-discovered TeV source are presented. The centroid of H. E. S. S. J1708-443 is considerably offset from the pulsar and located near the apparent center of the SNR, at alpha(J2000) = 17(h)08(m)11(s) +/- 17(s) and delta(J2000) = -44 degrees 20' +/- 4'. The source is found to be significantly more extended than the H. E. S. S. point spread function (similar to 0.1 degrees), with an intrinsic Gaussian width of 0.29 degrees +/- 0.04 degrees. Its integral flux between 1 and 10 TeV is similar to 3.8 x 10(-1)2 ph cm(-2) s(-1), equivalent to 17% of the Crab Nebula flux in the same energy range. The measured energy spectrum is well-fit by a power law with a relatively hard photon index Gamma = 2.0 +/- 0.1(stat) +/-0.2(sys). Additional multi-wavelength data, including 330 MHz VLA observations, were used to investigate the VHE gamma-ray source's possible associations with the pulsar wind nebula of PSR B1706-44 and/or with the complex radio structure of the partial shell-type SNR G 343.1-2.3.

  • 161. Abramowski, A.
    et al.
    Conrad, Jan
    Dickinson, Hugh
    Ripken, Joachim
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zechlin, H-S
    et al.,
    HESS OBSERVATIONS OF THE GLOBULAR CLUSTERS NGC 6388 AND M15 AND SEARCH FOR A DARK MATTER SIGNAL2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 735, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations of the globular clusters (GCs) NGC 6388 and M15 were carried out by the High Energy Stereoscopic System array of Cherenkov telescopes for a live time of 27.2 and 15.2 hr, respectively. No gamma-ray signal is found at the nominal target position of NGC 6388 and M15. In the primordial formation scenario, GCs are formed in a dark matter (DM) halo and DM could still be present in the baryon-dominated environment of GCs. This opens the possibility of observing a DM self-annihilation signal. The DM content of the GCs NGC 6388 and M15 is modeled taking into account the astrophysical processes that can be expected to influence the DM distribution during the evolution of the GC: the adiabatic contraction of DM by baryons, the adiabatic growth of a black hole in the DM halo, and the kinetic heating of DM by stars. Ninety-five percent confidence level exclusion limits on the DM particle velocity-weighted annihilation cross section are derived for these DM halos. In the TeV range, the limits on the velocity-weighted annihilation cross section are derived at the 10(-25) cm(3) s(-1) level and a few 10(-24) cm(3) s(-1) for NGC 6388 and M15, respectively.

  • 162. Abramowski, A.
    et al.
    Jacholkowska, A.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et al.,
    Search for Lorentz Invariance breaking with a likelihood fit of the PKS 2155-304 flare data taken on MJD 539442011Ingår i: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, nr 9, s. 738-747Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy scales approaching the Planck scale (similar to 10(19) GeV). With present photon data from the observations of distant astrophysical sources, it is possible to constrain the Lorentz Symmetry breaking linear term in the standard photon dispersion relations. Gamma Ray Bursts (GRB) and flaring Active Galactic Nuclei (AGN) are complementary to each other for this purpose, since they are observed at different distances in different energy ranges and with different levels of variability. Following a previous publication of the High Energy Stereoscopic System (H.E.S.S.) collaboration [1], a more sensitive event-by-event method consisting of a likelihood fit is applied to PKS 2155-304 flare data of MJD 53944 (July 28, 2006) as used in the previous publication. The previous limit on the linear term is improved by a factor of similar to 3 up to M-QG(1), > 2.1 X 10(1B) GeV and is currently the best result obtained with blazars. The sensitivity to the quadratic term is lower and provides a limit of M-QG(q) > 6.4 x 10(10) GeV, which is the best value obtained so far with an AGN and similar to the best limits obtained with GRB.

  • 163. Abramowski, A.
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et. al.,
    HESS J1943+213: a candidate extreme BL Lacertae object2011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 529, nr A49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ontext. The H.E.S.S. Cherenkov telescope array has been surveying the Galactic plane for new VHE (>100 GeV) gamma-ray sources.

    Aims. We report on a newly detected point-like source, HESS J1943+213. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts.

    Methods. We combine new H.E.S.S., Fermi/LAT and Nançay Radio Telescope observations with pre-existing non-simultaneous multi-wavelength observations of IGR J19443+2117 and discuss the likely source associations as well as the interpretation as an active galactic nucleus, a gamma-ray binary or a pulsar wind nebula.

    Results. HESS J1943+213 is detected at the significance level of 7.9σ (post-trials) at RA(J2000) = , Dec(J2000) = . The source has a soft spectrum with photon index Γ = 3.1 ± 0.3stat ± 0.2sys and a flux above 470 GeV of (1.3 ± 0.2stat ± 0.3sys) × 10-12 cm-2 s-1. There is no Fermi/LAT counterpart down to a flux limit of 6 × 10-9 cm-2 s-1 in the 0.1–100 GeV energy range (95% confidence upper limit calculated for an assumed power-law model with a photon index Γ = 2.0). The data from radio to VHE gamma-rays do not show any significant variability.

    Conclusions. The lack of a massive stellar counterpart disfavors the binary hypothesis, while the soft VHE spectrum would be very unusual in case of a pulsar wind nebula. In addition, the distance estimates for Galactic counterparts places them outside of the Milky Way. All available observations favor an interpretation as an extreme, high-frequency peaked BL Lac object with a redshift z > 0.14. This would be the first time a blazar is detected serendipitously from ground-based VHE observations, and the first VHE AGN detected in the Galactic Plane.

  • 164. Abramowski, A.
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    HESS Collaboration,
    et. al.,
    VHE gamma-ray emission of PKS 2155-304: spectral and temporal variability2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 520, s. A83-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Observations of very high-energy.-rays from blazars provide information about acceleration mechanisms occurring in their innermost regions. Studies of variability in these objects lead to a better understanding of the mechanisms in play.

    Aims. To investigate the spectral and temporal variability of VHE (>100 GeV) gamma-rays of the well-known high-frequency-peaked BL Lac object PKS 2155-304 with the HESS imaging atmospheric Cherenkov telescopes over a wide range of flux states.

    Methods. Data collected from 2005 to 2007 were analyzed. Spectra were derived on time scales ranging from 3 years to 4 min. Light curve variability was studied through doubling timescales and structure functions and compared with red noise process simulations.

    Results. The source was found to be in a low state from 2005 to 2007, except for a set of exceptional flares that occurred in July 2006. The quiescent state of the source is characterized by an associated mean flux level of (4.32 +/- 0.09(stat) +/- 0.86(syst)) x 10(-11) cm(-2) s(-1) above 200 GeV, or approximately 15% of the Crab Nebula, and a power-law photon index of Gamma = 3.53 +/- 0.06(stat) +/- 0.10(syst). During the flares of July 2006, doubling timescales of similar to 2 min are found. The spectral index variation is examined over two orders of magnitude in flux, yielding different behavior at low and high fluxes, which is a new phenomenon in VHE gamma-ray emitting blazars. The variability amplitude characterized by the fractional rms F-var is strongly energy-dependent and is proportional to E-0.19 +/- 0.01. The light curve rms correlates with the flux. This is the signature of a multiplicative process that can be accounted for as a red noise with a Fourier index of similar to 2.

    Conclusions. This unique data set shows evidence of a low-level.-ray emission state from PKS 2155-304 that possibly has a different origin than the outbursts. The discovery of the light curve ognormal behavior might be an indicator of the origin of aperiodic variability in blazars.

  • 165. Abramowski, A
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kawamura, A.
    et. al.,
    Revisiting the Westerlund 2 field with the HESS telescope array2011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 525, s. A46-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. Previous observations with the HESS telescope array revealed the existence of extended very-high-energy (VHE; E > 100 GeV) gamma-ray emission, HESS J1023-575, coincident with the young stellar cluster Westerlund 2. At the time of discovery, the origin of the observed emission was not unambiguously identified, and follow-up observations have been performed to further investigate the nature of this gamma-ray source. Methods. The Carina region towards the open cluster Westerlund 2 has been re-observed, increasing the total exposure to 45.9 h. The combined dataset includes 33 h of new data and now permits a search for energy-dependent morphology and detailed spectroscopy. Results. A new, hard spectrum VHE gamma-ray source, HESS J1026-582, was discovered with a statistical significance of 7 sigma. It is positionally coincident with the Fermi LAT pulsar PSRJ1028-5819. The positional coincidence and radio/gamma-ray characteristics of the LAT pulsar favors a scenario where the TeV emission originates from a pulsar wind nebula. The nature of HESS J1023-575 is discussed in light of the deep HESS observations and recent multi-wavelength discoveries, including the Fermi LAT pulsar PSRJ1022-5746 and giant molecular clouds in the region. Despite the improved VHE dataset, a clear identification of the object responsible for the VHE emission from HESS J1023-575 is not yet possible, and contribution from the nearby high-energy pulsar and/or the open cluster remains a possibility.

  • 166. Abramowski, A.
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zechlin, H. -S.
    et al.,
    A new SNR with TeV shell-type morphology: HESS J1731-3472011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 531, s. A81-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. The recent discovery of the radio shell-type supernova remnant (SNR), G353.6-0.7, in spatial coincidence with the unidentified TeV source HESS J1731-347 has motivated further observations of the source with the High Energy Stereoscopic System (HESS) Cherenkov telescope array to test a possible association of the gamma-ray emission with the SNR.

    Methods. With a total of 59 h of observation, representing about four times the initial exposure available in the discovery paper of HESS J1731-347, the gamma-ray morphology is investigated and compared with the radio morphology. An estimate of the distance is derived by comparing the interstellar absorption derived from X-rays and the one obtained from (12)CO and HI observations.

    Results. The deeper gamma-ray observation of the source has revealed a large shell-type structure with similar position and extension (r similar to 0.25 degrees) as the radio SNR, thus confirming their association. By accounting for the HESS angular resolution and projection effects within a simple shell model, the radial profile is compatible with a thin, spatially unresolved, rim. Together with RX J1713.7-3946, RX J0852.0-4622 and SN 1006, HESS J1731-347 is now the fourth SNR with a significant shell morphology at TeV energies. The derived lower limit on the distance of the SNR of 3.2 kpc is used together with radio and X-ray data to discuss the possible origin of the gamma-ray emission, either via inverse Compton scattering of electrons or the decay of neutral pions resulting from proton-proton interaction.

  • 167. Abramowski, A.
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zechlin, H. -S.
    et al.,
    HESS constraints on dark matter annihilations towards the sculptor and carina dwarf galaxies2011Ingår i: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, nr 8, s. 608-616Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Sculptor and Carina dwarf spheroidal galaxies were observed with the H.E.S.S. Cherenkov telescope array between January 2008 and December 2009. The data sets consist of a total of 11.8 h and 14.811 of high quality data, respectively. No gamma-ray signal was detected at the nominal positions of these galaxies above 220 GeV and 320 GeV, respectively. Upper limits on the gamma-ray fluxes at 95% CL assuming two forms for the spectral energy distribution (a power law shape and one derived from dark matter annihilation) are obtained at the level of 10(-13)-10(-12) cm(-2) s(-1) in the TeV range. Constraints on the velocity weighted dark matter particle annihilation cross section for both Sculptor and Carina dwarf galaxies range from <sigma v > 10(-21) cm(3) s(-1) down to <sigma v > similar to 10(-2)2 cm(3) s(-1) on the dark matter halo model used. Possible enhancements of the gamma-ray flux are studied: the Sommerfeld effect, which is found to exclude some dark matter particle masses, the internal Bremsstrahlung and clumps in the dark-matter halo distributions.

  • 168. Abramowski, A.
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zechlin, H-S.
    et al.,
    Very-high-energy gamma-ray emission from the direction of the Galactic globular cluster Terzan 52011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 531, s. L18-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The HESS very-high-energy (VHE, E > 0.1 TeV) gamma-ray telescope system has discovered a new source, HESS J1747-248. The measured integral flux is (1.2 +/- 0.3) x 10(-12) cm(-2) s(-1) above 440 GeV for a power-law photon spectral index of 2.5 +/- 0.3(stat) +/- 0.2(sys). The VHE gamma-ray source is located in the close vicinity of the Galactic globular cluster Terzan 5 and extends beyond the HESS point spread function (0.07 degrees). The probability of a chance coincidence with Terzan 5 and an unrelated VHE source is quite low (similar to 10(-4)). With the largest population of identified millisecond pulsars (msPSRs), a very high core stellar density and the brightest GeV range flux as measured by Fermi-LAT, Terzan 5 stands out among Galactic globular clusters. The properties of the VHE source are briefly discussed in the context of potential emission mechanisms, notably in relation to msPSRs. Interpretation of the available data accommodates several possible origins for this VHE gamma-ray source, although none of them offers a satisfying explanation of its peculiar morphology.

  • 169. Acciari, V. A.
    et al.
    Aliu, E.
    Arlen, T.
    Aune, T.
    Bautista, M.
    Beilicke, M.
    Benbow, W.
    Boettcher, M.
    Boltuch, D.
    Bradbury, S. M.
    Buckley, J. H.
    Bugaev, V.
    Byrum, K.
    Cannon, A.
    Cesarini, A.
    Chow, Y. C.
    Ciupik, L.
    Cogan, P.
    Cui, W.
    Duke, C.
    Falcone, A.
    Finley, J. P.
    Finnegan, G.
    Fortson, L.
    Furniss, A.
    Galante, N.
    Gall, D.
    Gillanders, G. H.
    Godambe, S.
    Grube, J.
    Guenette, R.
    Gyuk, G.
    Hanna, D.
    Holder, J.
    Hui, C. M.
    Humensky, T. B.
    Kaaret, P.
    Karlsson, N.
    Kertzman, M.
    Kieda, D.
    Konopelko, A.
    Krawczynski, H.
    Krennrich, F.
    Lang, M. J.
    LeBohec, S.
    Maier, G.
    McArthur, S.
    McCann, A.
    McCutcheon, M.
    Millis, J.
    Moriarty, P.
    Nagai, T.
    Ong, R. A.
    Otte, A. N.
    Pandel, D.
    Perkins, J. S.
    Pichel, A.
    Pohl, M.
    Quinn, J.
    Ragan, K.
    Reyes, L. C.
    Reynolds, P. T.
    Roache, E.
    Rose, H. J.
    Schroedter, M.
    Sembroski, G. H.
    Senturk, G. Demet
    Smith, A. W.
    Steele, D.
    Swordy, S. P.
    Theiling, M.
    Thibadeau, S.
    Varlotta, A.
    Vassiliev, V. V.
    Vincent, S.
    Wagner, R. G.
    Wakely, S. P.
    Ward, J. E.
    Weekes, T. C.
    Weinstein, A.
    Weisgarber, T.
    Williams, D. A.
    Wissel, S.
    Wood, M.
    Zitzer, B.
    Abdo, A. A.
    Ackermann, M.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Baughman, B. M.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Blandford, R. D.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Burnett, T. H.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Casandjian, J. M.
    Cavazzuti, E.
    Cecchi, C.
    Celik, Oe
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, J.
    Cutini, S.
    Dermer, C. D.
    de Angelis, A.
    de Palma, F.
    do Couto e Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Dumora, D.
    Farnier, C.
    Favuzzi, C.
    Fegan, S. J.
    Focke, W. B.
    Fortin, P.
    Frailis, M.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giebels, B.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hanabata, Y.
    Hays, E.
    Hughes, R. E.
    Jackson, Miranda
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kawai, N.
    Kerr, M.
    Knoedlseder, J.
    Kocian, M. L.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Makeev, A.
    Mazziotta, M. N.
    McEnery, J. E.
    Meurer, C.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Rodriguez, A. Y.
    Roth, M.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sadrozinski, H. F. -W
    Sanchez, D.
    Sander, A.
    Parkinson, P. M. Saz
    Scargle, J. D.
    Sgro, C.
    Shaw, M. S.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Strickman, M. S.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uchiyama, Y.
    Usher, T. L.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M.
    Barber, S. D.
    Terndrup, D. M.
    Discovery of very high energy gamma rays from PKS 1424+240 and multiwavelength constraints on ITS redshift2010Ingår i: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8205, Vol. 708, nr 2, s. L100-L106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the first detection of very high energy(83) (VHE) gamma-ray emission above 140 GeV from PKS 1424+240, a BL Lac object with an unknown redshift. The photon spectrum above 140 GeV measured by VERITAS is well described by a power law with a photon index of 3.8 +/- 0.5(stat) +/- 0.3(syst) and a flux normalization at 200 GeV of (5.1 +/- 0.9(stat) +/- 0.5(syst)) x 10(-11) TeV-1 cm(-2) s(-1), where stat and syst denote the statistical and systematical uncertainties, respectively. The VHE flux is steady over the observation period between MJD 54881 and 55003 (from 2009 February 19 to June 21). Flux variability is also not observed in contemporaneous high-energy observations with the Fermi Large Area Telescope. Contemporaneous X-ray and optical data were also obtained from the Swift XRT and MDM observatory, respectively. The broadband spectral energy distribution is well described by a one-zone synchrotron self-Compton model favoring a redshift of less than 0.1. Using the photon index measured with Fermi in combination with recent extragalactic background light absorption models it can be concluded from the VERITAS data that the redshift of PKS 1424+240 is less than 0.66.

  • 170. Acciari, V. A.
    et al.
    Aliu, E.
    Arlen, T.
    Aune, T.
    Bautista, M.
    Beilicke, M.
    Benbow, W.
    Boettcher, M.
    Boltuch, D.
    Bradbury, S. M.
    Buckley, J. H.
    Bugaev, V.
    Byrum, K.
    Cannon, A.
    Cesarini, A.
    Ciupik, L.
    Cui, W.
    Dickherber, R.
    Duke, C.
    Falcone, A.
    Finley, J. P.
    Finnegan, G.
    Fortson, L.
    Furniss, A.
    Galante, N.
    Gall, D.
    Gibbs, K.
    Gillanders, G. H.
    Godambe, S.
    Grube, J.
    Guenette, R.
    Gyuk, G.
    Hanna, D.
    Holder, J.
    Hui, C. M.
    Humensky, T. B.
    Imran, A.
    Kaaret, P.
    Karlsson, N.
    Kertzman, M.
    Kieda, D.
    Konopelko, A.
    Krawczynski, H.
    Krennrich, F.
    Lang, M. J.
    Lamerato, A.
    LeBohec, S.
    Maier, G.
    McArthur, S.
    McCann, A.
    McCutcheon, M.
    Moriarty, P.
    Mukherjee, R.
    Ong, R. A.
    Otte, A. N.
    Pandel, D.
    Perkins, J. S.
    Petry, D.
    Pichel, A.
    Pohl, M.
    Quinn, J.
    Ragan, K.
    Reyes, L. C.
    Reynolds, P. T.
    Roache, E.
    Rose, H. J.
    Roustazadeh, P.
    Schroedter, M.
    Sembroski, G. H.
    Senturk, G. Demet
    Smith, A. W.
    Steele, D.
    Swordy, S. P.
    Tesic, G.
    Theiling, M.
    Thibadeau, S.
    Varlotta, A.
    Vassiliev, V. V.
    Vincent, S.
    Wagner, R. G.
    Wakely, S. P.
    Ward, J. E.
    Weekes, T. C.
    Weinstein, A.
    Weisgarber, T.
    Williams, D. A.
    Wissel, S.
    Wood, M.
    Zitzer, B.
    Ackermann, M.
    Ajello, M.
    Antolini, E.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Blandford, R. D.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carrigan, S.
    Casandjian, J. M.
    Cavazzuti, E.
    Cecchi, C.
    Celik, Oe.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, J.
    Dermer, C. D.
    de Palma, F.
    do Couto e Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Farnier, C.
    Favuzzi, C.
    Fegan, S. J.
    Fortin, P.
    Frailis, M.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giebels, B.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Hays, E.
    Horan, D.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Garde, M. Llena
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Makeev, A.
    Mazziotta, M. N.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Ripken, J.
    Rodriguez, A. Y.
    Roth, M.
    Sadrozinski, H. F. -W
    Sanchez, D.
    Sander, A.
    Scargle, J. D.
    Sgro, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Strickman, M. S.
    Suson, D. J.
    Takahashi, H.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Usher, T. L.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M.
    THE DISCOVERY OF gamma-RAY EMISSION FROM THE BLAZAR RGB J0710+5912010Ingår i: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8205, Vol. 715, nr 1, s. L49-L55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high-frequency-peaked BL Lacertae object RGB J0710+591 was observed in the very high-energy (VHE; E > 100 GeV) wave band by the VERITAS array of atmospheric Cherenkov telescopes. The observations, taken between 2008 December and 2009 March and totaling 22.1 hr, yield the discovery of VHE gamma rays from the source. RGB J0710+591 is detected at a statistical significance of 5.5 standard deviations (5.5 sigma) above the background, corresponding to an integral flux of (3.9 +/- 0.8) x 10(-12) cm(-2) s(-1) (3% of the Crab Nebula's flux) above 300 GeV. The observed spectrum can be fit by a power law from 0.31 to 4.6 TeV with a photon spectral index of 2.69 +/- 0.26(stat) +/- 0.20(sys). These data are complemented by contemporaneous multiwavelength data from the Fermi Large Area Telescope, the Swift X-ray Telescope, the Swift Ultra-Violet and Optical Telescope, and the Michigan-Dartmouth-MIT observatory. Modeling the broadband spectral energy distribution (SED) with an equilibrium synchrotron self-Compton model yields a good statistical fit to the data. The addition of an external-Compton component to the model does not improve the fit nor brings the system closer to equipartition. The combined Fermi and VERITAS data constrain the properties of the high-energy emission component of the source over 4 orders of magnitude and give measurements of the rising and falling sections of the SED.

  • 171. Acero, F.
    et al.
    Aharonian, F.
    Akhperjanian, A. G.
    Anton, G.
    de Almeida, U. Barres
    Bazer-Bachi, A. R.
    Becherini, Y.
    Behera, B.
    Beilicke, M.
    Bernloehr, K.
    Bochow, A.
    Boisson, C.
    Bolmont, J.
    Borrel, V.
    Brucker, J.
    Brun, F.
    Brun, P.
    Buehler, R.
    Bulik, T.
    Buesching, I.
    Boutelier, T.
    Chadwick, P. M.
    Charbonnier, A.
    Chaves, R. C. G.
    Cheesebrough, A.
    Conrad, J.
    Chounet, L. -M
    Clapson, A. C.
    Coignet, G.
    Dalton, M.
    Daniel, M. K.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    Dickinson, H. J.
    Djannati-Atai, A.
    Domainko, W.
    Drury, L. O 'C.
    Dubois, F.
    Dubus, G.
    Dyks, J.
    Dyrda, M.
    Egberts, K.
    Eger, P.
    Espigat, P.
    Fallon, L.
    Farnier, C.
    Fegan, S.
    Feinstein, F.
    Fiasson, A.
    Foerster, A.
    Fontaine, G.
    Fuessling, M.
    Gabici, S.
    Gallant, Y. A.
    Gerard, L.
    Gerbig, D.
    Giebels, B.
    Glicenstein, J. F.
    Glueck, B.
    Goret, P.
    Goering, D.
    Hauser, D.
    Hauser, M.
    Heinz, S.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hinton, J. A.
    Hoffmann, A.
    Hofmann, W.
    Hofverberg, P.
    Holleran, M.
    Hoppe, S.
    Horns, D.
    Jacholkowska, A.
    de Jager, O. C.
    Jahn, C.
    Jung, I.
    Katarzynski, K.
    Katz, U.
    Kaufmann, S.
    Kerschhaggl, M.
    Khangulyan, D.
    Khelifi, B.
    Keogh, D.
    Klochkov, D.
    Kluzniak, W.
    Kneiske, T.
    Komin, Nu.
    Kosack, K.
    Kossakowski, R.
    Lamanna, G.
    Lemoine-Goumard, M.
    Lenain, J. -P
    Lohse, T.
    Marandon, V.
    Marcowith, A.
    Masbou, J.
    Maurin, D.
    McComb, T. J. L.
    Medina, M. C.
    Mehault, J.
    Moderski, R.
    Moulin, E.
    Naumann-Godo, M.
    de Naurois, M.
    Nedbal, D.
    Nekrassov, D.
    Nicholas, B.
    Niemiec, J.
    Nolan, S. J.
    Ohm, S.
    Olive, J. -F
    Wilhelmi, E. de Ona
    Orford, K. J.
    Ostrowski, M.
    Panter, M.
    Arribas, M. Paz
    Pedaletti, G.
    Pelletier, G.
    Petrucci, P. -O
    Pita, S.
    Puehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raubenheimer, B. C.
    Raue, M.
    Rayner, S. M.
    Reimer, O.
    Renaud, M.
    de los Reyes, R.
    Rieger, F.
    Ripken, J.
    Rob, L.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Ruppel, J.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sahakian, V.
    Santangelo, A.
    Schlickeiser, R.
    Schoeck, F. M.
    Schoenwald, A.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Shalchi, A.
    Sushch, I.
    Sikora, M.
    Skilton, J. L.
    Sol, H.
    Stawarz, L.
    Steenkamp, R.
    Stegmann, C.
    Stinzing, F.
    Superina, G.
    Szostek, A.
    Tam, P. H.
    Tavernet, J. -P
    Terrier, R.
    Tibolla, O.
    Tluczykont, M.
    van Eldik, C.
    Vasileiadis, G.
    Venter, C.
    Venter, L.
    Vialle, J. P.
    Vincent, P.
    Vink, J.
    Vivier, M.
    Voelk, H. J.
    Volpe, F.
    Vorobiov, S.
    Wagner, S. J.
    Ward, M.
    Zdziarski, A. A.
    Zech, A.
    First detection of VHE gamma-rays from SN 1006 by HESS2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 516, s. A62-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. Recent theoretical predictions of the lowest very high energy (VHE) luminosity of SN 1006 are only a factor 5 below the previously published HESS upper limit, thus motivating further in-depth observations of this source. Methods. Deep observations at VHE energies (above 100 GeV) were carried out with the high energy stereoscopic system (HESS) of Cherenkov Telescopes from 2003 to 2008. More than 100 h of data have been collected and subjected to an improved analysis procedure. Results. Observations resulted in the detection of VHE gamma-rays from SN 1006. The measured gamma-ray spectrum is compatible with a power-law, the flux is of the order of 1% of that detected from the Crab Nebula, and is thus consistent with the previously established HESS upper limit. The source exhibits a bipolar morphology, which is strongly correlated with non-thermal X-rays. Conclusions. Because the thickness of the VHE-shell is compatible with emission from a thin rim, particle acceleration in shock waves is likely to be the origin of the gamma-ray signal. The measured flux level can be accounted for by inverse Compton emission, but a mixed scenario that includes leptonic and hadronic components and takes into account the ambient matter density inferred from observations also leads to a satisfactory description of the multi-wavelength spectrum.

  • 172. Acero, F.
    et al.
    Aharonian, F.
    Akhperjanian, A. G.
    Anton, G.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zdziarski, A. A.
    Zech, A.
    Conrad, Jan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Localizing the VHE gamma-ray source at the Galactic Centre2010Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 402, nr 3, s. 1877-1882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The inner 10 pc of our Galaxy contains many counterpart candidates of the very high energy (VHE; > 100 GeV) gamma-ray point source HESS J1745-290. Within the point spread function of the H.E.S.S. measurement, at least three objects are capable of accelerating particles to VHE and beyond and of providing the observed gamma-ray flux. Previous attempts to address this source confusion were hampered by the fact that the projected distances between these objects were of the order of the error circle radius of the emission centroid (34 arcsec, dominated by the pointing uncertainty of the H.E.S.S. instrument). Here we present H.E.S.S. data of the Galactic Centre region, recorded with an improved control of the instrument pointing compared to H.E.S.S. standard pointing procedures. Stars observed during gamma-ray observations by optical guiding cameras mounted on each H.E.S.S. telescope are used for off-line pointing calibration, thereby decreasing the systematic pointing uncertainties from 20 to 6 arcsec per axis. The position of HESS J1745-290 is obtained by fitting a multi-Gaussian profile to the background-subtracted gamma-ray count map. A spatial comparison of the best-fitting position of HESS J1745-290 with the position and morphology of candidate counterparts is performed. The position is, within a total error circle radius of 13 arcsec, coincident with the position of the supermassive black hole Sgr A* and the recently discovered pulsar wind nebula candidate G359.95-0.04. It is significantly displaced from the centroid of the supernova remnant Sgr A East, excluding this object with high probability as the dominant source of the VHE gamma-ray emission.

  • 173. Acero, F.
    et al.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, Sweden.
    Li, L.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, Sweden.
    Zimmer, S.
    et al.,
    The first fermi lat supernova remnant catalog2016Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 224, nr 1, artikel-id 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope (LAT). Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude allows us to determine an upper limit of 22% on the number of GeV candidates falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, we demonstrate the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. We model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.

  • 174. Acero, F.
    et al.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zech, A.
    et al.,
    HESS upper limits on very high energy gamma-ray emission from the microquasar GRS 1915+1052009Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 508, nr 3, s. 1135-1140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. High energy particles reside in the relativistic jets of microquasars, making them possible sources of very high energy radiation (VHE, > 100 GeV). Detecting this emission would provide a new handle on jet physics.

    Aims. Observations of the microquasar GRS 1915+105 with the HESS telescope array were undertaken in 2004-2008 to search for VHE emission.

    Methods. Stereoscopic imaging of Cherenkov radiation from extensive air showers is used to reconstruct the energy and direction of the incident gamma rays.

    Results. There is no evidence for a VHE gamma-ray signal either from the direction of the microquasar or its vicinity. An upper limit of 6.1 x 10(-13) ph cm(-2) s(-1) (99.9% confidence level) is set on the photon flux above 410 GeV, equivalent to a VHE luminosity of similar to 10(34) erg s(-1) at 11 kpc.

    Conclusions. The VHE to X-ray luminosity ratio in GRS 1915+105 is at least four orders of magnitude lower than the ratio observed in gamma-ray binaries. The VHE radiative efficiency of the compact jet is less than 0.01% based on its estimated total power of 10(38) erg s(-1). Particle acceleration in GRS 1915+105 is not efficient at high energies and/or the magnetic field is too strong. It is also possible that VHE gamma-rays are produced by GRS 1915+105, but the emission is highly time-dependent.

  • 175.
    Acharya, Anshuman
    et al.
    Max-Planck-Institut für Astrophysik, Garching D-85748, Germany.
    Mertens, Florent
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Paris F-75014, France.
    Ciardi, Benedetta
    Max-Planck-Institut für Astrophysik, Garching D-85748, Germany.
    Ghara, Raghunath
    Astrophysics Research Centre, Open University of Israel, Ra'anana 4353701, Israel.
    Koopmans, Léon V.E.
    Kapteyn Astronomical Institute, University of Groningen, PO Box 800, Groningen NL-9700AV, the Netherlands, PO Box 800.
    Giri, Sambit K.
    Nordita SU.
    Hothi, Ian
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Paris F-75014, France; Laboratoire de Physique de l'ENS, ENS, Université PSL, CNRS, Sorbonne Université, Universitée Paris Cité, Paris F-75005, France.
    Ma, Qing Bo
    School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, P. R. China; Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing, Guizhou Normal University, Guiyang 550001, P. R. China.
    Mellema, Garrelt
    The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, Stockholm SE-10691, Sweden, AlbaNova.
    Munshi, Satyapan
    Kapteyn Astronomical Institute, University of Groningen, PO Box 800, Groningen NL-9700AV, the Netherlands, PO Box 800.
    21-cm signal from the Epoch of Reionization: a machine learning upgrade to foreground removal with Gaussian process regression2024Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 527, nr 3, s. 7835-7846Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent years, a Gaussian process regression (GPR)-based framework has been developed for foreground mitigation from data collected by the LOw-Frequency ARray (LOFAR), to measure the 21-cm signal power spectrum from the Epoch of Reionization (EoR) and cosmic dawn. However, it has been noted that through this method there can be a significant amount of signal loss if the EoR signal covariance is misestimated. To obtain better covariance models, we propose to use a kernel trained on the grizzly simulations using a Variational Auto-Encoder (VAE)-based algorithm. In this work, we explore the abilities of this machine learning-based kernel (VAE kernel) used with GPR, by testing it on mock signals from a variety of simulations, exploring noise levels corresponding to ≈10 nights (≈141 h) and ≈100 nights (≈1410 h) of observations with LOFAR. Our work suggests the possibility of successful extraction of the 21-cm signal within 2σ uncertainty in most cases using the VAE kernel, with better recovery of both shape and power than with previously used covariance models. We also explore the role of the excess noise component identified in past applications of GPR and additionally analyse the possibility of redshift dependence on the performance of the VAE kernel. The latter allows us to prepare for future LOFAR observations at a range of redshifts, as well as compare with results from other telescopes.

  • 176. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Anderson, B.
    Arimoto, M.
    Atwood, W. B.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Gonzalez, J. Becerra
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Britto, R. J.
    Bruel, P.
    Buehler, R.
    Burnett, T. H.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Casandjian, J. M.
    Cavazzuti, E.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Cohen-Tanugi, J.
    Cominsky, L. R.
    Condon, B.
    Costanza, F.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Lalla, N.
    Di Mauro, M.
    Di Venere, L.
    Dominguez, A.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Giglietto, N.
    Giomi, M.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Gomez-Vargas, G. A.
    Granot, J.
    Green, D.
    Grenier, I. A.
    Grondin, M. -H
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hadasch, D.
    Harding, A. K.
    Hays, E.
    Hewitt, J. W.
    Hill, A. B.
    Horan, D.
    Jogler, T.
    Johannesson, G.
    Kamae, T.
    Kensei, S.
    Kocevski, D.
    Kuss, M.
    La Mura, G.
    Larsson, S.
    Latronico, L.
    Lemoine-Goumard, M.
    Li, J.
    Li, L.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Magill, J.
    Maldera, S.
    Manfreda, A.
    Marelli, M.
    Mayer, M.
    Mazziotta, M. N.
    McEnery, J. E.
    Meyer, M.
    Michelson, P. F.
    Mirabal, N.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Moretti, E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Racusin, J. L.
    Raino, S.
    Rando, R.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Rochester, L. S.
    Romani, R. W.
    Parkinson, P. M. Saz
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Smith, D. A.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Troja, E.
    Uchiyama, Y.
    Venters, T. M.
    Vianello, G.
    Wood, K. S.
    Wood, M.
    Zaharijas, G.
    Zhu, S.
    Zimmer, S.
    FERMI-LAT OBSERVATIONS OF THE LIGO EVENT GW1509142016Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 823, nr 1, artikel-id L2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Fermi Large Area Telescope (LAT) has an instantaneous field of view (FoV) covering similar to 1/5 of the sky and it completes a survey of the entire sky in high-energy gamma-rays every 3 hr. It enables searches for transient phenomena over timescales from milliseconds to years. Among these phenomena could be electromagnetic counterparts to gravitational wave (GW) sources. In this paper, we present a detailed study of the LAT observations relevant to Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914, which is the first direct detection of gravitational waves and has been interpreted as being due to the coalescence of two stellar-mass black holes. The localization region for GW150914 was outside the LAT FoV at the time of the GW signal. However, as part of routine survey observations, the LAT observed the entire LIGO localization region within similar to 70 minutes of the trigger and thus enabled a comprehensive search for a.-ray counterpart to GW150914. The study of the LAT data presented here did not find any potential counterparts to GW150914, but it did provide limits on the presence of a transient counterpart above 100 MeV on timescales of hours to days over the entire GW150914 localization region.

  • 177. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, Jan
    KTH, Skolan för teknikvetenskap (SCI), Fysik. Stockholm University, Sweden.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Dermer, C. D.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Favuzzi, C.
    Ferrara, E. C.
    Focke, W. B.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Godfrey, G.
    Gomez-Vargas, G. A.
    Grenier, I. A.
    Guiriec, S.
    Gustafsson, M.
    Hadasch, D.
    Hayashi, K.
    Hays, E.
    Hewitt, J. W.
    Ippoliti, P.
    Jogler, T.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Kataoka, J.
    Knoedlseder, J.
    Kuss, M.
    Larsson, S.
    Latronico, L.
    Li, J.
    Li, L.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Manfreda, A.
    Massaro, F.
    Mayer, M.
    Mazziotta, M. N.
    McEnery, J. E.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nemmen, R.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Perkins, J. S.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Romani, R. W.
    Sanchez-Conde, M.
    Schaal, M.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Strong, A. W.
    Suson, D. J.
    Takahashi, H.
    Thayer, J. G.
    Thayer, J. B.
    Tibaldo, L.
    Tinivella, M.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Uchiyama, Y.
    Vianello, G.
    Werner, M.
    Winer, B. L.
    Wood, K. S.
    Wood, M.
    Zaharijas, G.
    Zimmer, S.
    The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 799, nr 1, s. 86-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The gamma-ray sky can be decomposed into individually detected sources, diffuse emission attributed to the interactions of Galactic cosmic rays with gas and radiation fields, and a residual all-sky emission component commonly called the isotropic diffuse gamma-ray background (IGRB). The IGRB comprises all extragalactic emissions too faint or too diffuse to be resolved in a given survey, as well as any residual Galactic foregrounds that are approximately isotropic. The first IGRB measurement with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) used 10 months of sky-survey data and considered an energy range between 200 MeV and 100 GeV. Improvements in event selection and characterization of cosmic-ray backgrounds, better understanding of the diffuse Galactic emission (DGE), and a longer data accumulation of 50 months allow for a refinement and extension of the IGRB measurement with the LAT, now covering the energy range from 100 MeV to 820 GeV. The IGRB spectrum shows a significant high-energy cutoff feature and can be well described over nearly four decades in energy by a power law with exponential cutoff having a spectral index of 2.32 +/- 0.02 and a break energy of (279 +/- 52) GeV using our baseline DGE model. The total intensity attributed to the IGRB is (7.2 +/- 0.6) x 10(-6) cm(-2) s(-1) sr(-1) above 100 MeV, with an additional +15%/-30% systematic uncertainty due to the Galactic diffuse foregrounds.

  • 178. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Atwood, W. B.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bonino, R.
    Bottacini, E.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Caliandro, G. A.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Costanza, F.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Venere, L.
    Drell, P. S.
    Favuzzi, C.
    Fegan, S. J.
    Focke, W. B.
    Franckowiak, A.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Harding, A. K.
    Hewitt, J. W.
    Horan, D.
    Hou, X.
    Iafrate, G.
    Johannesson, G.
    Kamae, T.
    Kuss, M.
    Larsson, S.
    Latronico, L.
    Li, J.
    Li, L.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Magill, J.
    Maldera, S.
    Manfreda, A.
    Mayer, M.
    Mazziotta, M. N.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Murgia, S.
    Nuss, E.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Pivato, G.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Sgro, C.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Takahashi, H.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Winer, B. L.
    Wood, K. S.
    Yassine, M.
    Measurement of the high-energy gamma-ray emission from the Moon with the Fermi Large Area Telescope2016Ingår i: PHYSICAL REVIEW D, ISSN 2470-0010, Vol. 93, nr 8, artikel-id 082001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first seven years of operation, in the energy range from 30 MeV up to a few GeV. We have also studied the time evolution of the flux, finding a correlation with the solar activity. We have developed a full Monte Carlo simulation describing the interactions of cosmic rays with the lunar surface. The results of the present analysis can be explained in the framework of this model, where the production of gamma rays is due to the interactions of cosmic-ray proton and helium nuclei with the surface of the Moon. Finally, we have used our simulation to derive the cosmic-ray proton and helium spectra near Earth from the Moon gamma-ray data.

  • 179. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiaro, G.
    Ciprini, S.
    Costanza, F.
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Lalla, N.
    Di Mauro, M.
    Di Venere, L.
    Favuzzi, C.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Green, D.
    Grenier, I. A.
    Guillemot, L.
    Guiriec, S.
    Hayashi, K.
    Hou, X.
    Johannesson, G.
    Kamae, T.
    Knodlseder, J.
    Kong, A. K. H.
    Kuss, M.
    La Mura, G.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Latronico, L.
    Li, J.
    Longo, F.
    Loparco, F.
    Lubrano, P.
    Maldera, S.
    Malyshev, D.
    Manfreda, A.
    Martin, P.
    Mazziotta, M. N.
    Michelson, P. F.
    Mirabal, N.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Persic, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Principe, G.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, O.
    Sanchez-Conde, M.
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Tanaka, K.
    Tibaldo, L.
    Torres, D. F.
    Troja, E.
    Uchiyama, Y.
    Wang, J. C.
    Wood, K. S.
    Wood, M.
    Zaharijas, G.
    Zhou, M.
    Observations of M31 and M33 with the Fermi Large Area Telescope: A Galactic Center Excess in Andromeda?2017Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 836, nr 2, artikel-id 208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Fermi Large Area Telescope (LAT) has opened the way for comparative studies of cosmic rays (CRs) and high-energy objects in the Milky Way (MW) and in other, external, star-forming galaxies. Using 2 yr of observations with the Fermi LAT, Local Group galaxy M31 was detected as a marginally extended gamma-ray source, while only an upper limit has been derived for the other nearby galaxy M33. We revisited the gamma-ray emission in the direction of M31 and M33 using more than 7 yr of LAT Pass 8 data in the energy range 0.1-100 GeV, presenting detailed morphological and spectral analyses. M33 remains undetected, and we computed an upper limit of 2.0 x 10(-12) erg cm(-2) s(-1) on the 0.1-100 GeV energy flux (95% confidence level). This revised upper limit remains consistent with the observed correlation between gamma-ray luminosity and star formation rate tracers and implies an average CR density in M33 that is at most half of that of the MW. M31 is detected with a significance of nearly 10 sigma. Its spectrum is consistent with a power law with photon index Gamma = 2.4 +/- 0.1(stat) (vertical bar) (syst) and a 0.1-100 GeV energy flux of (5.6 +/- 0.6(stat vertical bar syst)) x 10(-12) erg cm(-1) s(-1). M31 is detected to be extended with a 4 sigma significance. The spatial distribution of the emission is consistent with a uniform-brightness disk with a radius of 0 degrees.4 and no offset from the center of the galaxy, but nonuniform intensity distributions cannot be excluded. The flux from M31 appears confined to the inner regions of the galaxy and does not fill the disk of the galaxy or extend far from it. The gamma-ray signal is not correlated with regions rich in gas or star formation activity, which suggests that the emission is not interstellar in origin, unless the energetic particles radiating in gamma rays do not originate in recent star formation. Alternative and nonexclusive interpretations are that the emission results from a population of millisecond pulsars dispersed in the bulge and disk of M31 by disrupted globular clusters or from the decay or annihilation of dark matter particles, similar to what has been proposed to account for the so-called Galactic center excess found in Fermi-LAT observations of the MW.

  • 180. Ackermann, M.
    et al.
    Ajello, M.
    Allafort, A.
    Angelakis, E.
    Axelsson, Magnus
    Department of Astronomy, Stockholm University.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Berenji, B.
    Blandford, R. D.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Cannon, A.
    Caraveo, P. A.
    Casandjian, J. M.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Cutini, S.
    De Palma, F.
    Dermer, C. D.
    Do Couto E Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Escande, L.
    Favuzzi, C.
    Fegan, S. J.
    Focke, W. B.
    Fortin, P.
    Frailis, M.
    Fuhrmann, L.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grandi, P.
    Grenier, I. A.
    Guiriec, S.
    Hadasch, D.
    Hayashida, M.
    Hays, E.
    Healey, S. E.
    Jóhannesson, G.
    Johnson, A. S.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Knödlseder, J.
    Kuss, M.
    Lande, J.
    Lee, S. -H
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Makeev, A.
    Max-Moerbeck, W.
    Mazziotta, M. N.
    McEnery, J. E.
    Mehault, J.
    Michelson, P. F.
    Mizuno, T.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Naumann-Godo, M.
    Nishino, S.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paneque, D.
    Pavlidou, V.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Pierbattista, M.
    Piron, F.
    Porter, T. A.
    Rainò, S.
    Razzano, M.
    Readhead, A.
    Reimer, A.
    Reimer, O.
    Richards, J. L.
    Romani, R. W.
    Sadrozinski, H. F. -W
    Scargle, J. D.
    Sgrò, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Strickman, M. S.
    Suson, D. J.
    Takahashi, H.
    Tanaka, T.
    Taylor, G. B.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Troja, E.
    Vandenbroucke, J.
    Vianello, G.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Ziegler, M.
    The radio/gamma-ray connection in active galactic nuclei in the era of the fermi large area telescope2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 741, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose. We use both archival interferometric 8.4GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E &gt; 100MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of &lt;10 -7 for the correlation appearing by chance. Using the OVRO data, we find that concurrent data improve the significance of the correlation from 1.6 × 10-6 to 9.0 × 10-8. Our large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. We find that the correlation is very significant (chance probability &lt; 10-7) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.

  • 181. Ackermann, M.
    et al.
    Ajello, M.
    Allafort, A.
    Atwood, W. B.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Casandjian, J. M.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Cutini, S.
    De Palma, F.
    Dermer, C. D.
    Digel, S. W.
    Do Couto E Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Enoto, T.
    Falletti, L.
    Favuzzi, C.
    Fegan, S. J.
    Focke, W. B.
    Fortin, P.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Hadasch, D.
    Hayashida, M.
    Hays, E.
    Hughes, R. E.
    Jóhannesson, G.
    Johnson, A. S.
    Johnson, T. J.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Knödlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Mazziotta, M. N.
    McEnery, J. E.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakamori, T.
    Naumann-Godo, M.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pesce-Rollins, M.
    Pierbattista, M.
    Piron, F.
    Rain, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Rochester, L. S.
    Sgr, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Takahashi, H.
    Tanaka, T.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Tosti, G.
    Troja, E.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Zimmer, S.
    In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope2012Ingår i: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, nr 6, s. 346-353Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∌6 and ∌13 GeV with an estimated uncertainty of ∌2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

  • 182. Ackermann, M.
    et al.
    Ajello, M.
    Allafort, A.
    Atwood, W. B.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Bhat, P. N.
    Blandford, R. D.
    Bonamente, E.
    Borgland, A. W.
    Bregeon, J.
    Briggs, M. S.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Burgess, J. M.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Casandjian, J. M.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Connaughton, V.
    Conrad, J.
    Cutini, S.
    Dennis, B. R.
    de Palma, F.
    Dermer, C. D.
    Digel, S. W.
    Silva, E. d. C. e.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Fortin, P.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grillo, L.
    Grove, J. E.
    Gruber, D.
    Guiriec, S.
    Hadasch, D.
    Hayashida, M.
    Hays, E.
    Horan, D.
    Iafrate, G.
    Jóhannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Kippen, R. M.
    Knödlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Mazziotta, M. N.
    McEnery, J. E.
    Meegan, C.
    Mehault, J.
    Michelson, P. F.
    Mitthumsiri, W.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Murphy, R.
    Naumann-Godo, M.
    Nuss, E.
    Nymark, Tanja
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ohno, M.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Paciesas, W. S.
    Panetta, J. H.
    Parent, D.
    Pesce-Rollins, M.
    Petrosian, V.
    Pierbattista, M.
    Piron, F.
    Pivato, G.
    Poon, H.
    Porter, T. A.
    Preece, R.
    Rainò, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Ritz, S.
    Sbarra, C.
    Schwartz, R. A.
    Sgrò, C.
    Share, G. H.
    Siskind, E. J.
    Spinelli, P.
    Takahashi, H.
    Tanaka, T.
    Tanaka, Y.
    Thayer, J. B.
    Tibaldo, L.
    Tinivella, M.
    Tolbert, A. K.
    Tosti, G.
    Troja, E.
    Uchiyama, Y.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Vitale, V.
    von Kienlin, A.
    Waite, A. P.
    Wilson-Hodge, C.
    Wood, D. L.
    Wood, K. S.
    Yang, Z.
    Fermi Detection of γ-Ray Emission from the M2 Soft X-Ray Flare on 2010 June 122012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 745, nr 2, s. 144-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Geostationary Operational Environmental Satellite (GOES) M2-class solar flare, SOL2010-06-12T00: 57, was modest in many respects yet exhibited remarkable acceleration of energetic particles. The flare produced an similar to 50 s impulsive burst of hard X-and gamma-ray emission up to at least 400 MeV observed by the Fermi Gamma-ray Burst Monitor and Large Area Telescope experiments. The remarkably similar hard X-ray and high-energy gamma-ray time profiles suggest that most of the particles were accelerated to energies greater than or similar to 300 MeV with a delay of similar to 10 s from mildly relativistic electrons, but some reached these energies in as little as similar to 3 s. The gamma-ray line fluence from this flare was about 10 times higher than that typically observed from this modest GOES class of X-ray flare. There is no evidence for time-extended >100 MeV emission as has been found for other flares with high-energy gamma-rays.

  • 183. Ackermann, M.
    et al.
    Ajello, M.
    Allafort, A.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Blandford, R. D.
    Blasi, P.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Brandt, T. J.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carrigan, S.
    Casandjian, J. M.
    Cavazzuti, E.
    Cecchi, C.
    Celik, Oe
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Colafrancesco, S.
    Cominsky, L. R.
    Conrad, J.
    Dermer, C. D.
    de Palma, F.
    Silva, E. do Couto e
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Edmonds, Y.
    Farnier, C.
    Favuzzi, C.
    Frailis, M.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grondin, M. -H
    Guiriec, S.
    Hadasch, D.
    Harding, A. K.
    Hayashida, M.
    Hays, E.
    Horan, D.
    Hughes, R. E.
    Jeltema, T. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, T. J.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kerr, M.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Lemoine-Goumard, M.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Makeev, A.
    Mazziotta, M. N.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Naumann-Godo, M.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paneque, D.
    Panetta, J. H.
    Pepe, M.
    Pesce-Rollins, M.
    Petrosian, V.
    Pfrommer, C.
    Piron, F.
    Porter, T. A.
    Profumo, S.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ripken, J.
    Ritz, S.
    Rodriguez, A. Y.
    Romani, R. W.
    Roth, M.
    Sadrozinski, H. F. -W
    Sander, A.
    Parkinson, P. M. Saz
    Scargle, J. D.
    Sgro, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Starck, J. -L
    Stawarz, L.
    Strickman, M. S.
    Strong, A. W.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Tibaldo, L.
    Tibolla, O.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uchiyama, Y.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ziegler, M.
    GeV GAMMA-RAY FLUX UPPER LIMITS FROM CLUSTERS OF GALAXIES2010Ingår i: ASTROPHYS J LETT, ISSN 2041-8205, Vol. 717, nr 1, s. L71-L78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The detection of diffuse radio emission associated with clusters of galaxies indicates populations of relativistic leptons infusing the intracluster medium (ICM). Those electrons and positrons are either injected into and accelerated directly in the ICM, or produced as secondary pairs by cosmic-ray ions scattering on ambient protons. Radiation mechanisms involving the energetic leptons together with the decay of neutral pions produced by hadronic interactions have the potential to produce abundant GeV photons. Here, we report on the search for GeV emission from clusters of galaxies using data collected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope from 2008 August to 2010 February. Thirty-three galaxy clusters have been selected according to their proximity and high mass, X-ray flux and temperature, and indications of non-thermal activity for this study. We report upper limits on the photon flux in the range 0.2-100 GeV toward a sample of observed clusters (typical values (1-5) x 10(-9) photon cm(-2) s(-1)) considering both point-like and spatially resolved models for the high-energy emission and discuss how these results constrain the characteristics of energetic leptons and hadrons, and magnetic fields in the ICM. The volume-averaged relativistic-hadron-to-thermal energy density ratio is found to be <5%-10% in several clusters.

  • 184. Ackermann, M.
    et al.
    Ajello, M.
    Asano, K.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Bhat, P. N.
    Bissaldi, E.
    Bloom, E. D.
    Bonamente, E.
    Bonnell, J.
    Bouvier, A.
    Brandt, T. J.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Burgess, J. Michael
    Buson, S.
    Byrne, D.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cecchi, C.
    Charles, E.
    Chaves, R. C. G.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Connaughton, V.
    Conrad, J.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Dermer, C. D.
    Desiante, R.
    Digel, S. W.
    Dingus, B. L.
    Di Venere, L.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Favuzzi, C.
    Ferrara, E. C.
    Fitzpatrick, G.
    Foley, S.
    Franckowiak, A.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Goldstein, A.
    Granot, J.
    Grenier, I. A.
    Grove, J. E.
    Gruber, D.
    Guiriec, S.
    Hadasch, D.
    Hanabata, Y.
    Hayashida, M.
    Horan, D.
    Hou, X.
    Hughes, R. E.
    Inoue, Y.
    Jackson, Miranda S.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Jogler, T.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Kataoka, J.
    Kawano, T.
    Kippen, R. M.
    Knoedlseder, J.
    Kocevski, D.
    Kouveliotou, C.
    Kuss, M.
    Lande, J.
    Larsson, S.
    Latronico, L.
    Lee, S. -H
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Massaro, F.
    Mayer, M.
    Mazziotta, M. N.
    McBreen, S.
    McEnery, J. E.
    McGlynn, S.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Morselli, A.
    Murgia, S.
    Nemmen, R.
    Nuss, E.
    Nymark, Tanja
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ohno, M.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Paciesas, W. S.
    Paneque, D.
    Panetta, J. H.
    Pelassa, V.
    Perkins, J. S.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Preece, R.
    Racusin, J. L.
    Raino, S.
    Rando, R.
    Rau, A.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Romoli, C.
    Roth, M.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Parkinson, P. M. Saz
    Schalk, T. L.
    Sgro, C.
    Siskind, E. J.
    Sonbas, E.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Takeuchi, Y.
    Tanaka, Y.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Tierney, D.
    Tinivella, M.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Tronconi, V.
    Usher, T. L.
    Vandenbroucke, J.
    van der Horst, A. J.
    Vasileiou, V.
    Vianello, G.
    Vitale, V.
    von Kienlin, A.
    Winer, B. L.
    Wood, K. S.
    Wood, M.
    Xiong, S.
    Yang, Z.
    The first Fermi-Lat gamma-ray burst catalog2013Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 209, nr 1, s. 11-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy (greater than or similar to 20 MeV) gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above similar to 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  • 185. Ackermann, M.
    et al.
    Ajello, M.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Baughman, B. M.
    Bechtol, K.
    Bellardi, F.
    Bellazzini, R.
    Belli, F.
    Berenji, B.
    Blandford, R. D.
    Bloom, E. D.
    Bogart, J. R.
    Bonamente, E.
    Borgland, A. W.
    Brandt, T. J.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Burnett, T. H.
    Busetto, G.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Carrigan, S.
    Casandjian, J. M.
    Ceccanti, M.
    Cecchi, C.
    Celik, Oe
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Cillis, A. N.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, J.
    Corbet, R.
    DeKlotz, M.
    Dermer, C. D.
    de Angelis, A.
    de Palma, F.
    Digel, S. W.
    Di Bernardo, G.
    do Couto e Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Fabiani, D.
    Favuzzi, C.
    Fegan, S. J.
    Fortin, P.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gaggero, D.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grasso, D.
    Grenier, I. A.
    Grondin, M. -H
    Grove, J. E.
    Guiriec, S.
    Gustafsson, M.
    Hadasch, D.
    Harding, A. K.
    Hayashida, M.
    Hays, E.
    Horan, D.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, R. P.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kerr, M.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lemoine-Goumard, M.
    Garde, M. Llena
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Makeev, A.
    Mazziotta, M. N.
    McEnery, J. E.
    Mehault, J.
    Michelson, P. F.
    Minuti, M.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Moretti, Elena
    University and INFN of Trieste.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakamori, T.
    Naumann-Godo, M.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Petrosian, V.
    Pinchera, M.
    Piron, F.
    Porter, T. A.
    Profumo, S.
    Raino, S.
    Rando, R.
    Rapposelli, E.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ripken, J.
    Ritz, S.
    Rochester, L. S.
    Romani, R. W.
    Roth, M.
    Sadrozinski, H. F. -W
    Saggini, N.
    Sanchez, D.
    Sander, A.
    Sgro, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Stawarz, L.
    Stephens, T. E.
    Strickman, M. S.
    Strong, A. W.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Tibolla, O.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Turri, M.
    Uchiyama, Y.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wallace, E.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M.
    Fermi LAT observations of cosmic-ray electrons from 7 GeV to 1 TeV2010Ingår i: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 82, nr 9, s. 092004-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of our analysis of cosmic-ray electrons using about 8 x 10(6) electron candidates detected in the first 12 months on-orbit by the Fermi Large Area Telescope. This work extends our previously published cosmic-ray electron spectrum down to 7 GeV, giving a spectral range of approximately 2.5 decades up to 1 TeV. We describe in detail the analysis and its validation using beam-test and on-orbit data. In addition, we describe the spectrum measured via a subset of events selected for the best energy resolution as a cross-check on the measurement using the full event sample. Our electron spectrum can be described with a power law proportional to E-3.08+/-0.05 with no prominent spectral features within systematic uncertainties. Within the limits of our uncertainties, we can accommodate a slight spectral hardening at around 100 GeV and a slight softening above 500 GeV.

  • 186. Ackermann, M.
    et al.
    Ajello, M.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Burnett, T. H.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carrigan, S.
    Casandjian, J. M.
    Cecchi, C.
    Celik, Oe
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Conrad, J.
    Cuoco, A.
    Dermer, C. D.
    de Angelis, A.
    de Palma, F.
    Digel, S. W.
    Di Bernardo, G.
    do Couto e Silva, E.
    Drell, P. S.
    Dubois, R.
    Favuzzi, C.
    Fegan, S. J.
    Focke, W. B.
    Frailis, M.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gaggero, D.
    Gargano, F.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grasso, D.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Gustafsson, M.
    Hadasch, D.
    Harding, A. K.
    Hayashi, K.
    Hays, E.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kerr, M.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Lemoine-Goumard, M.
    Garde, M. Llena
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Makeev, A.
    Mazziotta, M. N.
    McEnery, J. E.
    Mehault, J.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakamori, T.
    Naumann-Godo, M.
    Nolan, P. L.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Profumo, S.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ripken, J.
    Ritz, S.
    Roth, M.
    Sadrozinski, H. F. -W
    Sander, A.
    Schalk, T. L.
    Sgro, C.
    Siegal-Gaskins, J.
    Siskind, E. J.
    Smith, D. A.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Strickman, M. S.
    Strong, A. W.
    Suson, D. J.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uchiyama, Y.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zaharijas, G.
    Ziegler, M.
    Searches for cosmic-ray electron anisotropies with the Fermi Large Area Telescope2010Ingår i: PHYS REV D, ISSN 1550-7998, Vol. 82, nr 9, s. 092003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Large Area Telescope on board the Fermi satellite (Fermi LAT) detected more than 1.6 x 10(6) cosmic-ray electrons/positrons with energies above 60 GeV during its first year of operation. The arrival directions of these events were searched for anisotropies of angular scale extending from similar to 10 degrees up to 90 degrees, and of minimum energy extending from 60 GeV up to 480 GeV. Two independent techniques were used to search for anisotropies, both resulting in null results. Upper limits on the degree of the anisotropy were set that depended on the analyzed energy range and on the anisotropy's angular scale. The upper limits for a dipole anisotropy ranged from similar to 0.5% to similar to 10%.

  • 187. Ackermann, M.
    et al.
    Ajello, M.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Gonzalez, J. Becerra
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Cohen, J. M.
    Cohen-Tanugi, J.
    Cominsky, L. R.
    Conrad, J.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Di Mauro, M.
    Di Venere, L.
    Dominguez, A.
    Drell, P. S.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Focke, W. B.
    Fortin, P.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Furniss, A. K.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grondin, M. -H
    Guillemot, L.
    Guiriec, S.
    Harding, A. K.
    Hays, E.
    Hewitt, J. W.
    Hill, A. B.
    Horan, D.
    Iafrate, G.
    Hartmann, Dieter
    Jogler, T.
    Johannesson, G.
    Johnson, A. S.
    Kamae, T.
    Kataoka, J.
    Knoedlseder, J.
    Kuss, M.
    La Mura, G.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Latronico, L.
    Lemoine-Goumard, M.
    Li, J.
    Li, L.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Maldera, S.
    Manfreda, A.
    Mayer, M.
    Mazziotta, M. N.
    Michelson, P. F.
    Mirabal, N.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Romani, R. W.
    Sanchez-Conde, M.
    Parkinson, P. M. Saz
    Schmid, J.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Takahashi, M.
    Takahashi, T.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Wood, K. S.
    Wood, M.
    Yassine, M.
    Zaharijas, G.
    Zimmer, S.
    2FHL: THE SECOND CATALOG OF HARD FERMI-LAT SOURCES2016Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 222, nr 1, artikel-id 5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass. 8 event-level analysis allows the detection and characterization of sources in the 50 GeV-2 TeV energy range. In this energy band, Fermi-LAT. has detected 360 sources, which constitute the second catalog of hard Fermi-LAT. sources (2FHL). The improved angular resolution enables the precise localization of point sources (similar to 1.' 7 radius at 68% C.L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associated with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi-LAT. on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.

  • 188. Ackermann, M.
    et al.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bhat, P. N.
    Bissaldi, E.
    Blandford, R. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Briggs, M. S.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carrigan, S.
    Casandjian, J. M.
    Cecchi, C.
    Celik, Oe
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Connaughton, V.
    Conrad, J.
    Cutini, S.
    Dermer, C. D.
    de Angelis, A.
    de Palma, F.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Dubois, R.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Frailis, M.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Granot, J.
    Grenier, I. A.
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hadasch, D.
    Hays, E.
    Horan, D.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kippen, R. M.
    Knoedlseder, J.
    Kocevski, D.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Garde, M. Llena
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Makeev, A.
    Mazziotta, M. N.
    McBreen, S.
    McEnery, J. E.
    McGlynn, S.
    Meegan, C.
    Mehault, J.
    Meszaros, P.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Moretti, Elena
    University and INFN of Trieste.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakajima, H.
    Nakamori, T.
    Naumann-Godo, M.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paciesas, W. S.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Porter, T. A.
    Preece, R.
    Racusin, J. L.
    Raino, S.
    Rando, R.
    Rau, A.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Ripken, J.
    Roth, M.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sadrozinski, H. F. -W
    Sander, A.
    Scargle, J. D.
    Schalk, T. L.
    Sgro, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Stamatikos, M.
    Strickman, M. S.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uehara, T.
    Usher, T. L.
    Vandenbroucke, J.
    van der Horst, A. J.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    von Kienlin, A.
    Waite, A. P.
    Wang, P.
    Wilson-Hodge, C.
    Winer, B. L.
    Wood, K. S.
    Wu, X. F.
    Yamazaki, R.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ziegler, M.
    FERMI OBSERVATIONS OF HIGH-ENERGY GAMMA-RAY EMISSION FROM GRB 090217A2010Ingår i: ASTROPHYS J LETT, ISSN 2041-8205, Vol. 717, nr 2, s. L127-L132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Fermi observatory is advancing our knowledge of gamma-ray bursts (GRBs) through pioneering observations at high energies, covering more than seven decades in energy with the two on-board detectors, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Here, we report on the observation of the long GRB 090217A which triggered the GBM and has been detected by the LAT with a significance greater than 9 sigma. We present the GBM and LAT observations and on-ground analyses, including the time-resolved spectra and the study of the temporal profile from 8 keV up to similar to 1 GeV. All spectra are well reproduced by a Band model. We compare these observations to the first two LAT-detected, long bursts GRB 080825C and GRB 080916C. These bursts were found to have time-dependent spectra and exhibited a delayed onset of the high-energy emission, which are not observed in the case of GRB 090217A. We discuss some theoretical implications for the high-energy emission of GRBs.

  • 189. Ackermann, M.
    et al.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Blandford, R. D.
    Bonamente, E.
    Borgland, A. W.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Burnett, T. H.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carrigan, S.
    Casandjian, J. M.
    Cavazzuti, E.
    Cecchi, C.
    Celik, Oe
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Corbel, S.
    Cutini, S.
    D'Ammando, F.
    Dermer, C. D.
    de Angelis, A.
    de Palma, F.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Escande, L.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Fuhrmann, L.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giebels, B.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Hadasch, D.
    Hayashida, M.
    Hays, E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Larsson, S.
    Latronico, L.
    Lee, S. -H
    Garde, M. Llena
    Longo, F.
    Loparco, F.
    Lott, B.
    Lubrano, P.
    Madejski, G. M.
    Makeev, A.
    Marchili, N.
    Mazziotta, M. N.
    McEnery, J. E.
    Mehault, J.
    Michelson, P. F.
    Mizuno, T.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakamori, T.
    Nalewajko, K.
    Naumann-Godo, M.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reyes, L. C.
    Ripken, J.
    Ritz, S.
    Roth, M.
    Sadrozinski, H. F. -W
    Sanchez, D.
    Sander, A.
    Scargle, J. D.
    Sgro, C.
    Sikora, M.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Strickman, M. S.
    Suson, D. J.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Tanaka, Y.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Usher, T. L.
    Vandenbroucke, J.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Wehrle, A. E.
    Winer, B. L.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden; School of Pure and Applied Natural Sciences, University of Kalmar, SE-391 82 Kalmar, Sweden.
    Ziegler, M.
    Fermi gamma-ray space telescope observations of gamma-ray outbursts from 3C 454.3 in 2009 december and 2010 april2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 721, nr 2, s. 1383-1396Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The flat spectrum radio quasar 3C 454.3 underwent an extraordinary outburst in 2009 December when it became the brightest gamma-ray source in the sky for over 1 week. Its daily flux measured with the Fermi-Large Area Telescope at photon energiesE > 100 MeV reached F-100 = 22 +/- 1 x 10(6) photon cm(-2) s(-1), representing the highest daily flux of any blazar ever recorded in high-energy. -rays. It again became the brightest source in the sky in 2010 April, triggering a pointed-mode observation by Fermi. The correlated. -ray temporal and spectral properties during these exceptional events are presented and discussed. The main results show flux variability over time scales less than 3 hr and very mild spectral variability with an indication of gradual hardening preceding major flares. The light curves during periods of enhanced activity in 2008 July-August and 2010 December show strong resemblance, with a flux plateau of a few days preceding the major flare. No consistent loop pattern emerged in the. -ray spectral index versus the flux plane as would be expected in acceleration and cooling scenarios. The maximum energy of a photon from 3C 454.3 is approximate to 20 GeV and a minimum Doppler factor of approximate to 13 is derived. The gamma-ray spectrum of 3C 454.3 shows a significant spectral break between approximate to 2 and 3 GeV that is very weakly dependent on the flux state, even when the flux changes by an order of magnitude.

  • 190. Ackermann, M.
    et al.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Camilo, F.
    Caraveo, P. A.
    Casandjian, J. M.
    Cecchi, C.
    Celik, Oe.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cognard, I.
    Cohen-Tanugi, J.
    Conrad, J.
    Dermer, C. D.
    de Angelis, A.
    de Luca, A.
    de Palma, F.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Favuzzi, C.
    Focke, W. B.
    Frailis, M.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Germani, S.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grondin, M. -H
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hadasch, D.
    Hanabata, Y.
    Harding, A. K.
    Hayashi, K.
    Hays, E.
    Hobbs, G.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, W. N.
    Johnston, S.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Keith, M.
    Kerr, M.
    Knoedlseder, J.
    Kramer, M.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Lemoine-Goumard, M.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Lyne, A. G.
    Makeev, A.
    Marelli, M.
    Mazziotta, M. N.
    McEnery, J. E.
    Mehault, J.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakamori, T.
    Naumann-Godo, M.
    Nolan, P. L.
    Noutsos, A.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Ransom, S. M.
    Ray, P. S.
    Razzano, M.
    Rea, N.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ripken, J.
    Ritz, S.
    Romani, R. W.
    Sadrozinski, H. F. -W
    Sander, A.
    Parkinson, P. M. Saz
    Sgro, C.
    Siskind, E. J.
    Smith, D. A.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Strickman, M. S.
    Suson, D. J.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Theureau, G.
    Thompson, D. J.
    Thorsett, S. E.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uchiyama, Y.
    Uehara, T.
    Usher, T. L.
    Vandenbroucke, J.
    Van Etten, A.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Weltevrede, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Ziegler, M.
    Fermi-LAT search for pulsar wind nebulae around gamma-ray pulsars2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 726, nr 1, s. 35-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high sensitivity of the Fermi-LAT (Large Area Telescope) offers the first opportunity to study faint and extended GeV sources such as pulsar wind nebulae (PWNe). After one year of observation the LAT detected and identified three PWNe: the Crab Nebula, Vela-X, and the PWN inside MSH 15-52. In the meantime, the list of LAT detected pulsars increased steadily. These pulsars are characterized by high energy loss rates ((E) over dot) from similar to 3 x 10(33) erg s(-1) to 5 x 10(38) erg s(-1) and are therefore likely to power a PWN. This paper summarizes the search for PWNe in the off-pulse windows of 54 LAT-detected pulsars using 16 months of survey observations. Ten sources show significant emission, seven of these likely being of magnetospheric origin. The detection of significant emission in the off-pulse interval offers new constraints on the gamma-ray emitting regions in pulsar magnetospheres. The three other sources with significant emission are the Crab Nebula, Vela-X, and a new PWN candidate associated with the LAT pulsar PSR J1023-5746, coincident with the TeV source HESS J1023-575. We further explore the association between the HESS and the Fermi source by modeling its spectral energy distribution. Flux upper limits derived for the 44 remaining sources are used to provide new constraints on famous PWNe that have been detected at keV and/or TeV energies.

  • 191. Ackermann, M.
    et al.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiaro, G.
    Ciprini, S.
    Cohen, J. M.
    Cohen-Tanugi, J.
    Costanza, F.
    Cutini, S.
    D'Ammando, F.
    Davis, D. S.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Lalla, N.
    Di Mauro, M.
    Di Venere, L.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Focke, W. B.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Georganopoulos, M.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Godfrey, G.
    Green, D.
    Grenier, I. A.
    Guiriec, S.
    Hays, E.
    Hewitt, J. W.
    Hill, A. B.
    Jogler, T.
    Johnnesson, G.
    Kensei, S.
    Kuss, M.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Latronico, L.
    Li, J.
    Li, L.
    Longo, F.
    Loparco, F.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Manfreda, A.
    Mayer, M.
    Mazziotta, M. N.
    McConville, W.
    McEnery, J. E.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Negro, M.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Schmid, J.
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Stawarz, L.
    Takahashi, H.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Wood, K. S.
    Wood, M.
    Zimmer, S.
    FERMI LARGE AREA TELESCOPE DETECTION OF EXTENDED GAMMA-RAY EMISSION FROM THE RADIO GALAXY FORNAX A2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 826, nr 1, artikel-id 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the Fermi Large Area Telescope detection of extended gamma-ray emission from the lobes of the radio galaxy Fornax. A using 6.1 years of Pass. 8 data. After Centaurus. A, this is now the second example of an extended gamma-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to be < 14% of the total gamma-ray flux. A preferred alignment of the gamma-ray elongation with the radio lobes was demonstrated by rotating the radio lobes template. We found no significant evidence for variability on similar to 0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the gamma-rays. With the extended nature of the > 100 MeV gamma-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus. A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the gamma-ray fluxes by factors of about similar to 2-3, depending on the EBL model adopted. An additional gamma-ray spectral component is thus required, and could be due to hadronic emission arising from proton-proton collisions of cosmic rays with thermal plasma within the radio lobes.

  • 192. Ackermann, M.
    et al.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Gonzalez, J. B.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Cheung, C. C.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Conrad, J.
    Costantin, D.
    Costanza, F.
    Cutini, S.
    D'Ammando, F.
    Palma, F. D.
    Desiante, R.
    Digel, S. W.
    Lalla, N. D.
    Mauro, M. D.
    Venere, L. D.
    Domínguez, A.
    Drell, P. S.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Finke, J.
    Focke, W. B.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Green, D.
    Grenier, I. A.
    Guillemot, L.
    Guiriec, S.
    Hartmann, D. H.
    Hays, E.
    Horan, D.
    Jogler, T.
    Jóhannesson, G.
    Johnson, A. S.
    Kuss, M.
    Mura, G. L.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Latronico, L.
    Li, J.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Manfreda, A.
    Marcotulli, L.
    Mazziotta, M. N.
    Michelson, P. F.
    Mirabal, N.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Ojha, R.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paliya, V. S.
    Paneque, D.
    Perkins, J. S.
    Persic, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Principe, G.
    Rainò, S.
    Rando, R.
    Rani, B.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Romani, R. W.
    Sgrò, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Stalin, C. S.
    Stawarz, L.
    Suson, D. J.
    Takahashi, M.
    Tanaka, K.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Torresi, E.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Wood, K. S.
    Gamma-Ray Blazars within the First 2 Billion Years2017Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 837, nr 1, artikel-id L5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The detection of high-redshift (z &gt; 3) blazars enables the study of the evolution of the most luminous relativistic jets over cosmic time. More importantly, high-redshift blazars tend to host massive black holes and can be used to constrain the space density of heavy black holes in the early universe. Here, we report the first detection with the Fermi-Large Area Telescope of five γ-ray-emitting blazars beyond z = 3.1, more distant than any blazars previously detected in γ-rays. Among these five objects, NVSS J151002+570243 is now the most distant known γ-ray-emitting blazar at z = 4.31. These objects have steeply falling γ-ray spectral energy distributions (SEDs), and those that have been observed in X-rays have a very hard X-ray spectrum, both typical of powerful blazars. Their Compton dominance (ratio of the inverse Compton to synchrotron peak luminosities) is also very large (&gt;20). All of these properties place these objects among the most extreme members of the blazar population. Their optical spectra and the modeling of their optical-UV SEDs confirm that these objects harbor massive black holes (MBH ∼ 10 8-10 Mo ). We find that, at z ≈ 4, the space density of &gt;109 Mo black holes hosted in radio-loud and radio-quiet active galactic nuclei are similar, implying that radio-loudness may play a key role in rapid black hole growth in the early universe.

  • 193. Ackermann, M
    et al.
    Ajello, M
    McGlynn, Sinead
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M
    et al.,
    DETECTION OF A SPECTRAL BREAK IN THE EXTRA HARD COMPONENT OF GRB 090926A2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 729, nr 2, s. nr 114-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.

  • 194. Ackermann, M.
    et al.
    Albert, A.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Bloom, E. D.
    Bonino, R.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Caliandro, G. A.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Cohen-Tanugi, J.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Drell, P. S.
    Favuzzi, C.
    Ferrara, E. C.
    Focke, W. B.
    Franckowiak, A.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Godfrey, G.
    Grenier, I. A.
    Grondin, M. -H
    Guillemot, L.
    Guiriec, S.
    Harding, A. K.
    Hill, A. B.
    Horan, D.
    Johannesson, G.
    Knoedlseder, J.
    Kuss, M.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Oskar Klein Centre for Cosmoparticle Physics, Alba Nova, Sweden.
    Latronico, L.
    Li, J.
    Li, Liang
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Oskar Klein Centre for Cosmoparticle Physics, Alba Nova, Sweden.
    Longo, F.
    Loparco, F.
    Lubrano, P.
    Maldera, S.
    Martin, P.
    Mayer, M.
    Mazziotta, M. N.
    Michelson, P. F.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Murgia, S.
    Nuss, E.
    Ohsugi, T.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Romani, R. W.
    Sanchez-Conde, M.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Smith, D. A.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Takahashi, H.
    Thayer, J. B.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Wood, M.
    Zimmer, S.
    Deep view of the Large Magellanic Cloud with six years of Fermi-LAT observations2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 586, artikel-id A71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The nearby Large Magellanic Cloud (LMC) provides a rare opportunity of a spatially resolved view of an external star-forming galaxy in gamma-rays. The LMC was detected at 0.1-100 GeV as an extended source with CGRO/EGRET and using early observations with the Fermi-LAT. The emission was found to correlate with massive star-forming regions and to be particularly bright towards 30 Doradus. Aims. Studies of the origin and transport of cosmic rays (CRs) in the Milky Way are frequently hampered by line-of-sight confusion and poor distance determination. The LMC offers a complementary way to address these questions by revealing whether and how the gamma-ray emission is connected to specific objects, populations of objects, and structures in the galaxy. Methods. We revisited the gamma-ray emission from the LMC using about 73 months of Fermi-LAT P7REP data in the 0.2-100 GeV range. We developed a complete spatial and spectral model of the LMC emission, for which we tested several approaches: a simple geometrical description, template-fitting, and a physically driven model for CR-induced interstellar emission. Results. In addition to identifying PSR J0540-6919 through its pulsations, we find two hard sources positionally coincident with plerion N 157B and supernova remnant N 132D, which were also detected at TeV energies with H.E.S.S. We detect an additional soft source that is currently unidentified. Extended emission dominates the total flux from the LMC. It consists of an extended component of about the size of the galaxy and additional emission from three to four regions with degree-scale sizes. If it is interpreted as CRs interacting with interstellar gas, the large-scale emission implies a large-scale population of similar to 1-100 GeV CRs with a density of similar to 30% of the local Galactic value. On top of that, the three to four small-scale emission regions would correspond to enhancements of the CR density by factors 2 to 6 or higher, possibly more energetic and younger populations of CRs compared to the large-scale population. An alternative explanation is that this is emission from an unresolved population of at least two dozen objects, such as pulsars and their nebulae or supernova remnants. This small-scale extended emission has a spatial distribution that does not clearly correlate with known components of the LMC, except for a possible relation to cavities and supergiant shells. Conclusions. The Fermi-LAT GeV observations allowed us to detect individual sources in the LMC. Three of the newly discovered sources are associated with rare and extreme objects. The 30 Doradus region is prominent in GeV gamma-rays because PSR J0540-6919 and N 157B are strong emitters. The extended emission from the galaxy has an unexpected spatial distribution, and observations at higher energies and in radio may help to clarify its origin.

  • 195. Ackermann, M.
    et al.
    Allafort, A.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Bonino, R.
    Bottacini, E.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Ciprini, S.
    Costanza, F.
    Cutini, S.
    D'Ammando, F.
    Palma, F. D.
    Desiante, R.
    Digel, S. W.
    Lalla, N. D.
    Mauro, M. D.
    Venere, L. D.
    Drell, P. S.
    Favuzzi, C.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Grenier, I. A.
    Guillemot, L.
    Guiriec, S.
    Jogler, T.
    Jóhannesson, G.
    Kashapova, L.
    Krucker, S.
    Kuss, M.
    Mura, G. L.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Latronico, L.
    Li, J.
    Liu, W.
    Longo, F.
    Loparco, F.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Manfreda, A.
    Mazziotta, M. N.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Pal'Shin, V.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Principe, G.
    Rainò, S.
    Rando, R.
    Razzano, M.
    Reimer, O.
    Costa, F. R. D.
    Sgrò, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Tajima, H.
    Thayer, J. B.
    Torres, D. F.
    Troja, E.
    Vianello, G.
    Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares2017Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 835, nr 2, artikel-id 219Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwave spectra. We also provide a comparison of the BTL flares detected by Fermi-LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.

  • 196. Ackermann, M.
    et al.
    Asano, K.
    Atwood, W. B.
    Axelsson, Magnus
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bhat, P. N.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Briggs, M. S.
    Brigida, M.
    Bruel, P.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Carrigan, S.
    Casandjian, J. M.
    Cecchi, C.
    Celik, Oe.
    Charles, E.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Connaughton, V.
    Conrad, J.
    Dermer, C. D.
    de Palma, F.
    Dingus, B. L.
    do Couto e Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Farnier, C.
    Favuzzi, C.
    Fegan, S. J.
    Finke, J.
    Focke, W. B.
    Frailis, M.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Glanzman, T.
    Godfrey, G.
    Granot, J.
    Grenier, I. A.
    Grondin, M. -H
    Grove, J. E.
    Guiriec, S.
    Hadasch, D.
    Harding, A. K.
    Hays, E.
    Horan, D.
    Hughes, R. E.
    Johannesson, G.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kawai, N.
    Kippen, R. M.
    Knoedlseder, J.
    Kocevski, D.
    Kouveliotou, C.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lemoine-Goumard, M.
    Garde, M. Llena
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Makeev, A.
    Mazziotta, M. N.
    McEnery, J. E.
    McGlynn, Sinéad
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Meegan, C.
    Meszaros, P.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Moretti, Elena
    University and INFN of Trieste.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakajima, H.
    Nakamori, T.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paciesas, W. S.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Preece, R.
    Raino, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Ritz, S.
    Rodriguez, A. Y.
    Roth, M.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Sadrozinski, H. F. -W
    Sander, A.
    Scargle, J. D.
    Schalk, T. L.
    Sgro, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Stamatikos, M.
    Stecker, F. W.
    Strickman, M. S.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Toma, K.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uchiyama, Y.
    Uehara, T.
    Usher, T. L.
    van der Horst, A. J.
    Vasileiou, V.
    Vilchez, N.
    Vitale, V.
    von Kienlin, A.
    Waite, A. P.
    Wang, P.
    Wilson-Hodge, C.
    Winer, B. L.
    Wu, X. F.
    Yamazaki, R.
    Yang, Z.
    Ylinen, Tomi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ziegler, M.
    Fermi observations of GRB 090510: A short-hard gamma-ray burst with an additional, hard power-law component from 10 keV to GeV energies2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 716, nr 2, s. 1178-1190Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present detailed observations of the bright short-hard gamma-ray burst GRB 090510 made with the Gammaray Burst Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi observatory. GRB 090510 is the first burst detected by the LAT that shows strong evidence for a deviation from a Band spectral fitting function during the prompt emission phase. The time-integrated spectrum is fit by the sum of a Band function with E-peak = 3.9 +/- 0.3 MeV, which is the highest yet measured, and a hard power-law component with photon index -1.62 +/- 0.03 that dominates the emission below approximate to 20 keV and above approximate to 100 MeV. The onset of the high-energy spectral component appears to be delayed by similar to 0.1 s with respect to the onset of a component well fit with a single Band function. A faint GBM pulse and a LAT photon are detected 0.5 s before the main pulse. During the prompt phase, the LAT detected a photon with energy 30.5(-2.6)(+5.8) GeV, the highest ever measured from a short GRB. Observation of this photon sets a minimum bulk outflow Lorentz factor, Gamma greater than or similar to 1200, using simple.. opacity arguments for this GRB at redshift z = 0.903 and a variability timescale on the order of tens of ms for the approximate to 100 keV-few MeV flux. Stricter high confidence estimates imply Gamma greater than or similar to 1000 and still require that the outflows powering short GRBs are at least as highly relativistic as those of long-duration GRBs. Implications of the temporal behavior and power-law shape of the additional component on synchrotron/synchrotron self-Compton, external-shock synchrotron, and hadronic models are considered.

  • 197. Ackermann, M
    et al.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Tokyo Metropolitan University, Japan.
    Wood, K. S.
    et al.,
    FERMI LAT STACKING ANALYSIS OF SWIFT LOCALIZED GRBs2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 822, nr 2, artikel-id 68Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We perform a comprehensive stacking analysis of data collected by the Fermi. Large Area Telescope (LAT) of gamma-ray bursts (GRBs) localized by the Swift. spacecraft, which were not detected by the LAT but which fell within the instrument's field of view at the time of trigger. We examine a total of 79 GRBs by comparing the observed counts over a range of time intervals to that expected from designated background orbits, as well as by using a joint likelihood technique to model the expected distribution of stacked counts. We find strong evidence for subthreshold emission at MeV to GeV energies using both techniques. This observed excess is detected during intervals that include and exceed the durations typically characterizing the prompt emission observed at keV energies and lasts at least 2700 s after the co-aligned burst trigger. By utilizing a novel cumulative likelihood analysis, we find that although a burst's prompt gamma-ray and afterglow X-ray flux both correlate with the strength of the subthreshold emission, the X-ray afterglow flux measured by Swift's X-ray Telescope at 11 hr post trigger correlates far more significantly. Overall, the extended nature of the subthreshold emission and its connection to the burst's afterglow brightness lend. further support to the external forward shock origin of the late-time emission detected by the LAT. These results suggest that the extended high-energy emission observed by the LAT may be a relatively common feature but remains undetected in a majority of bursts owing. to instrumental threshold effects.

  • 198. Ackermann, M.
    et al.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zimmer, S
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    THE SECOND CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 743, nr 2, s. 171-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The second LAT AGN catalog (2LAC) includes 1017 gamma-ray sources located at high Galactic latitudes (vertical bar b vertical bar > 10 degrees) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a Clean Sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency < 10(14) Hz, about half of the BL Lac objects have a synchrotron-peak frequency > 10(15) Hz. The 2LAC represents a significant improvement relative to the first LAT AGN catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broadband data. Various properties, such as gamma-ray fluxes and photon power-law spectral indices, redshifts, gamma-ray luminosities, variability, and archival radio luminosities and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.

  • 199. Ackermann, M.
    et al.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.
    Li, L.
    et al.,
    Multiwavelength evidence for quasi-periodic modulation in the gamma-ray blazar PG 1553+1132015Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 813, nr 2, artikel-id L41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report for the first time a γ-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 ± 0.08 year period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in ∼10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.

  • 200. Ackermann, M.
    et al.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.
    Li, L.
    et al.,
    SEARCH for EXTENDED GAMMA-RAY EMISSION from the VIRGO GALAXY CLUSTER with FERMI-LAT2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 812, nr 2, artikel-id 159Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Galaxy clusters are one of the prime sites to search for dark matter (DM) annihilation signals. Depending on the substructure of the DM halo of a galaxy cluster and the cross sections for DM annihilation channels, these signals might be detectable by the latest generation of gamma-ray telescopes. Here we use three years of Fermi-Large Area Telescope data, which are the most suitable for searching for very extended emission in the vicinity of the nearby Virgo galaxy cluster. Our analysis reveals statistically significant extended emission which can be well characterized by a uniformly emitting disk profile with a radius of 3 degrees that moreover is offset from the cluster center. We demonstrate that the significance of this extended emission strongly depends on the adopted interstellar emission model (IEM) and is most likely an artifact of our incomplete description of the IEM in this region. We also search for and find new point source candidates in the region. We then derive conservative upper limits on the velocity-averaged DM pair annihilation cross section from Virgo. We take into account the potential gamma-ray flux enhancement due to DM sub-halos and its complex morphology as a merging cluster. For DM annihilating into b (b) over bar, assuming a conservative sub-halo model setup, we find limits that are between 1 and 1.5 orders of magnitude above the expectation from the thermal cross section for m(DM) <= 100 GeV. In a more optimistic scenario, we exclude <sigma v > similar to 3 x 10(-26)cm(3)s(-1) for m(DM)less than or similar to 40 GeV for the same channel. Finally, we derive upper limits on the gamma-ray-flux produced by hadronic cosmic-ray interactions in the inter cluster medium. We find that the volume-averaged cosmic-ray-to-thermal pressure ratio is less than similar to 6%.

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