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  • 201.
    Ahlgren, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Investigating subphotospheric dissipation in gamma-ray bursts by fitting a physical model2019Doktoravhandling, med artikler (Annet vitenskapelig)
  • 202.
    Ahlgren, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Subphotospheric dissipation in gamma-ray bursts observed by the Fermi Gamma-ray Space Telescope2016Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Gamma-ray bursts (GRBs) are the brightest events in the Universe, for a short time outshining the rest of the Universe combined, as they explode with isotropic equivalent luminosities up to $10^{54}$ erg s$^{-1}$. These events are believed to be connected to supernovae and to binary compact object mergers, such as binary neutron stars or neutron star -- black hole systems. The origin of the so-called prompt emission in GRBs remains an unsolved problem, although some progress is being made. Spectral analysis of prompt emission has traditionally been performed with the Band function, an empirical model with no physical interpretation, and it is just recently that physical models have started to be fitted to data. This thesis presents spectral analysis of GRB data from the Fermi Gamma-ray Space Telescope using a physical model for subphotospheric dissipation. The model is developed using a numerical code and implemented as a table model in {\scriptsize XSPEC}. Paper \rom{1} presents the model and provides a proof-of-concept of fitting GRB data with such a model. Specifically, two GRBs are fitted and compared with the corresponding Band function fits. In paper \rom{2}, a sample of 37 bursts are fitted with an extended version of the model and improved analysis tools. Overall, about a third of the fitted spectra can be described by the model. From these fits it is concluded that the scenario of subphotospheric dissipation can describe all spectral shapes present in the sample. The key characteristic of the spectra that are not fitted by the model is that they are very luminous. Within the context of the model, this suggests that the assumption of internal shocks as a dissipation mechanism cannot explain the full population of GRBs. Alternatively, additional emission components may required. The thesis concludes that subphotospheric dissipation is viable as a possible origin of GRB prompt emission. Furthermore, it shows the importance of using physically motivated models when analysing GRBs.

  • 203.
    Ahlgren, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario and reveal correlationsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

     The emission mechanisms that give rise to the prompt emission in gamma-ray bursts (GRBs) is one of the main open questions in understanding these extreme explosions.

    We consider a model for subphotospheric dissipation which produces non-thermal spectra from the photosphere, by letting kinetic energy of the outow dissipate below the photosphere using a dissipation mechanism based on internal shocks. Building on the work of Ahlgren et al. (2015), we expand the model parameter space, compensate for adiabatic cooling, and improve the analysis tools. We create two table models for two dierent scenarios regarding the magnetisation, corresponding to no and moderate synchrotron emission, respectively. We t the models to time-resolved spectra of a sample of 37 Fermi GRBs and nd that  approximately a third of the spectra can be described by the models. From these ts we conclude that the scenario of subphotospheric dissipation can describe all spectral shapes present in the sample. However, we are not able to discriminate between no and moderate synchrotron emission. The key characteristic of spectra which are not tted by the model is that they are very luminous. Within the context of our model, we conclude that this is due to the assumption of internal shocks as a dissipation mechanism. Alternatively, some of these luminous bursts may require additional emission components.

  • 204.
    Ahlgren, Björn
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ahlberg, Erik
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lundman, Christoffer
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pe'er, Asaf
    Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario2019Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, s. 474-497Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has been suggested that the prompt emission in gamma-ray bursts (GRBs) could be described by radiation from the photosphere in a hot fireball. Such models must be tested by directly fitting them to data. In this work we use data from the Fermi Gamma-ray Space Telescope and consider a specific photospheric model, in which the kinetic energy of a low-magnetization outflow is dissipated locally by internal shocks below the photosphere. We construct a table model with a physically motivated parameter space and fit it to time-resolved spectra of the 36 brightest Fermi GRBs with a known redshift. We find that about two-thirds of the examined spectra cannot be described by the model, as it typically underpredicts the observed flux. However, since the sample is strongly biased towards bright GRBs, we argue that this fraction will be significantly lowered when considering the full population. From the successful fits we find that the model can reproduce the full range of spectral slopes present in the sample. For these cases we also find that the dissipation consistently occurs at a radius of ∼1012 cm and that only a few per cent efficiency is required. Furthermore, we find a positive correlation between the fireball luminosity and the Lorentz factor. Such a correlation has been previously reported by independent methods. We conclude that if GRB spectra are due to photospheric emission, the dissipation cannot only be the specific scenario we consider here.

  • 205.
    Ahlgren, Björn
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Larsson, Josefin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Valan, Vlasta
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Mortlock, Daniel
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pe'er, Asaf
    Constraining subphotospheric dissipation in Gamma-ray Bursts using joint Fermi-Swift observationsManuskript (preprint) (Annet vitenskapelig)
  • 206.
    Ahnen, M. L.
    et al.
    Swiss Fed Inst Technol, CH-8093 Zurich, Switzerland..
    Jóhannesson, Gudlaugur
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Yassine, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    et al.,
    MAGIC and Fermi-LAT gamma-ray results on unassociated HAWC sources2019Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, nr 1, s. 356-366Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The HAWC Collaboration released the 2HWC catalogue of TeV sources, in which 19 show no association with any known high-energy (HE; E greater than or similar to 10 GeV) or very-high-energy (VHE; E greater than or similar to 300 GeV) sources. This catalogue motivated follow-up studies by both the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) and Fermi-LAT (Large Area Telescope) observatories with the aim of investigating gamma-ray emission over a broad energy band. In this paper, we report the results from the first joint work between High Altitude Water Cherenkov (HAWC), MAGIC, and Fermi-LAT on three unassociated HAWC sources: 2HWC J2006+341, 2HWC J1907+084*, and 2HWC J1852+013*. Although no significant detection was found in the HE and VHE regimes, this investigation shows that a minimum 1 degrees extension (at 95 per cent confidence level) and harder spectrum in the GeV than the one extrapolated from HAWC results are required in the case of 2HWC J1852+013*, whilst a simply minimum extension of 0.16 degrees (at 95 per cent confidence level) can already explain the scenario proposed by HAWC for the remaining sources. Moreover, the hypothesis that these sources are pulsar wind nebulae is also investigated in detail.

  • 207. Ahnen, Max L.
    et al.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, Stockholm, Sweden.
    Li, Liang
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, Stockholm, Sweden.
    Zottmann, N.
    et al.,
    VERY HIGH ENERGY γ-RAYS from the UNIVERSE'S MIDDLE AGEMAGIC: DETECTION of the z = 0.940 BLAZAR PKS 1441+25 with MAGIC2015Inngår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 815, nr 2, artikkel-id L23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability timescale is estimated to be 6.4 ±1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad-line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.

  • 208. Ajello, M.
    et al.
    Albert, A.
    Allafort, A.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Bonamente, E.
    Brandt, T. J.
    Bregeon, J.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Cominsky, L. R.
    Conrad, J.
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Dermer, C. D.
    Desiante, R.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Favuzzi, C.
    Focke, W. B.
    Franckowiak, A.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Germani, S.
    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.
    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.
    Knoedlseder, J.
    Kocevski, D.
    Kuss, M.
    Lande, J.
    Larsson, S.
    Latronico, L.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Mayer, 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.
    Murphy, R.
    Nakamori, T.
    Nemmen, R.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Perkins, J. S.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Roth, M.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Takahashi, H.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Tinivella, M.
    Tosti, G.
    Troja, E.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Vitale, V.
    Werner, M.
    Winer, B. L.
    Wood, D. L.
    Wood, K. S.
    Yang, Z.
    Impulsive and long duration high-energy gamma-ray emission from the very bright 2012 march 7 solar flares2014Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 789, nr 1, s. 20-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Fermi Large Area Telescope (LAT) detected gamma-rays up to 4 GeV from two bright X-class solar flares on 2012 March 7, showing both an impulsive and temporally extended emission phases. The gamma-rays appear to originate from the same active region as the X-rays associated with these flares. The >100 MeV gamma-ray flux decreases monotonically during the first hour (impulsive phase) followed by a slower decrease for the next 20 hr. A power law with a high-energy exponential cutoff can adequately describe the photon spectrum. Assuming that the gamma rays result from the decay of pions produced by accelerated protons and ions with a power-law spectrum, we find that the index of that spectrum is similar to 3, with minor variations during the impulsive phase. During the extended phase the photon spectrum softens monotonically, requiring the proton index varying from similar to 4 to >5. The >30 MeV proton flux observed by the GOES satellites also shows a flux decrease and spectral softening, but with a harder spectrum (index similar to 2-3). Based on these observations, we explore the relative merits of prompt or continuous acceleration scenarios, hadronic or leptonic emission processes, and acceleration at the solar corona or by the fast coronal mass ejections. We conclude that the most likely scenario is continuous acceleration of protons in the solar corona that penetrate the lower solar atmosphere and produce pions that decay into gamma rays. However, acceleration in the downstream of the shock cannot be definitely ruled out.

  • 209. Ajello, M.
    et al.
    Albert, A.
    Atwood, W. B.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    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.
    Carave, P. A.
    Cecchi, C.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Cohen-Tanugi, J.
    Cominsky, L. R.
    Conrad, J.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Di Venere, L.
    Drell, P. S.
    Favuzzi, C.
    Ferrara, E. C.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Gomez-Vargas, G. A.
    Grenier, I. A.
    Guiriec, S.
    Gustafsson, M.
    Harding, A. K.
    Hewitt, J. W.
    Hill, A. B.
    Horan, D.
    Jogler, T.
    Johannesson, G.
    Johnson, A. S.
    Kamae, T.
    Karwin, C.
    Knoedlseder, J.
    Kuss, M.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Latronico, L.
    Li, J.
    Li, L.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Magill, J.
    Maldera, S.
    Malyshev, D.
    Manfreda, A.
    Mayer, M.
    Mazziotta, M. N.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Omodei, N.
    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.
    Ritz, S.
    Sanchez-Conde, M.
    Parkinson, P. M. Saz
    Sgro, C.
    Siskind, E. J.
    Smith, D. A.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Thayer, J. B.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Uchiyama, Y.
    Vianello, G.
    Winer, B. L.
    Wood, K. S.
    Zaharijas, G.
    Zimmer, S.
    FERMI-LAT OBSERVATIONS OF HIGH-ENERGY gamma-RAY EMISSION TOWARD THE GALACTIC CENTER2016Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 819, nr 1, artikkel-id 44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy gamma-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1-100 GeV from a 15 degrees x 15 degrees region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the.-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner similar to 1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15 degrees x 15 degrees region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with gamma-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.

  • 210. Ajello, M.
    et al.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bregeon, J.
    Britto, R. J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiaro, G.
    Ciprini, S.
    Cohen, J. M.
    Costantin, D.
    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.
    Dumora, D.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Fortin, P.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Green, D.
    Grenier, I. A.
    Grondin, M. -H
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Harding, A. K.
    Hays, E.
    Hewitt, J. W.
    Horan, D.
    Jóhannesson, Gudlaugur
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Kensei, S.
    Kuss, M.
    La Mura, G.
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Latronico, L.
    Lemoine-Goumard, M.
    Li, J.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Manfreda, A.
    Mazziotta, M. N.
    McEnery, J. E.
    Meyer, M.
    Michelson, P. F.
    Mirabal, N.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Palatiello, M.
    Paliya, V. S.
    Paneque, D.
    Perkins, J. S.
    Persic, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Principe, G.
    Raino, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Parkinson, P. M. Saz
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Stawarz, L.
    Suson, D. J.
    Takahashi, M.
    Tak, D.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Torresi, E.
    Troja, E.
    Vianello, G.
    Wood, K.
    Wood, M.
    3FHL: The Third Catalog of Hard Fermi-LAT Sources2017Inngår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 232, nr 2, artikkel-id 18Artikkel i tidsskrift (Fagfellevurdert)
  • 211.
    Ajello, M.
    et al.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Baldini, L.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Barbiellini, G.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Bastieri, D.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Bellazzini, R.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Bissaldi, E.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Blandford, R. D.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Bonino, R.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Turin, Dipartimento Fis, I-10125 Turin, Italy..
    Bottacini, E.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Bregeon, J.
    Univ Montpellier, CNRS IN2P3, Lab Univers & Particules Montpellier, F-34095 Montpellier, France..
    Bruel, P.
    CNRS IN2P3, Ecole Polytech, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Buehler, R.
    DESY, D-15738 Zeuthen, Germany..
    Cameron, R. A.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Caputo, R.
    CRESST, Greenbelt, MD 20771 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Caraveo, P. A.
    INAF Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Chiaro, G.
    INAF Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Ciprini, S.
    Agenzia Spaziale Italiana, Space Sci Data Ctr, Via Politecn, I-00133 Rome, Italy..
    Cohen-Tanugi, J.
    Univ Montpellier, CNRS IN2P3, Lab Univers & Particules Montpellier, F-34095 Montpellier, France..
    Costantin, D.
    Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    D'Ammando, F.
    INAF Ist Radioastron, I-40129 Bologna, Italy.;Univ Bologna, Dipartimento Astron, I-40127 Bologna, Italy..
    de Palma, F.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy.;Univ Telemat Pegaso, Piazza Trieste & Trento 48, I-80132 Naples, Italy..
    Di Lalla, N.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Di Mauro, M.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Di Venere, L.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Dominguez, A.
    Univ Complutense Madrid, Grp Altas Energias, E-28040 Madrid, Spain..
    Favuzzi, C.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Franckowiak, A.
    DESY, D-15738 Zeuthen, Germany..
    Fukazawa, Y.
    Hiroshima Univ, Dept Phys Sci, Higashihiroshima, Hiroshima 7398526, Japan..
    Funk, S.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Fusco, P.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Gargano, F.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Gasparrini, D.
    Agenzia Spaziale Italiana, Space Sci Data Ctr, Via Politecn, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Giglietto, N.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giordano, F.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giroletti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Green, D.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Grenier, I. A.
    Univ Paris Diderot, Lab AIM, CEA IRFU, CNRS,Serv Astrophys,CEA Saclay, F-91191 Gif Sur Yvette, France..
    Guiriec, S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;George Washington Univ, Dept Phys, 725 21st St NW, Washington, DC 20052 USA..
    Holt, C.
    Univ Maryland Baltimore Cty, Dept Phys, Baltimore, MD 21250 USA.;Univ Maryland Baltimore Cty, Ctr Space Sci & Technol, Baltimore, MD 21250 USA..
    Horan, D.
    CNRS IN2P3, Ecole Polytech, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Johannesson, G.
    Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;NORDITA, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Kocevski, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Kuss, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    La Mura, G.
    Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Li, J.
    Inst Space Sci CSICIEEC, Campus UAB,Carrer Magrans S-N, E-08193 Barcelona, Spain..
    Longo, F.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Loparco, F.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Lubrano, P.
    Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Magill, J. D.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Maldera, S.
    Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Manfreda, A.
    Univ Pisa, I-56127 Pisa, Italy..
    Mazziotta, M. N.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Michelson, P. F.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Mizuno, T.
    Hiroshima Univ, Hiroshima Astrophys Sci Ctr, Higashihiroshima, Hiroshima 7398526, Japan..
    Monzani, M. E.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Morselli, A.
    Ist Nazl Fis Nucl, Sez Roma Tor Vergata, I-00133 Rome, Italy..
    Negro, M.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Turin, Dipartimento Fis, I-10125 Turin, Italy..
    Nuss, E.
    Univ Montpellier, CNRS IN2P3, Lab Univers & Particules Montpellier, F-34095 Montpellier, France..
    Omodei, N.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Orienti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Orlando, E.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Paliya, V. S.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Perkins, J. S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Persic, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Ist Nazl Astrofis, Osservatorio Astron Trieste, I-34143 Trieste, Italy..
    Pesce-Rollins, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Piron, F.
    Univ Montpellier, CNRS IN2P3, Lab Univers & Particules Montpellier, F-34095 Montpellier, France..
    Principe, G.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Racusin, J. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Raino, S.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Rando, R.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Razzano, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Razzaque, S.
    Univ Johannesburg, Dept Phys, POB 524, ZA-2006 Auckland Pk, South Africa..
    Reimer, A.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA.;Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria..
    Reimer, O.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA.;Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria..
    Sgro, C.
    Siskind, E. J.
    NYCB Real Time Comp Inc, Lattingtown, NY 11560 USA..
    Spandre, G.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Spinelli, P.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Tak, D.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Thayer, J. B.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Torres, D. F.
    ICREA, E-08010 Barcelona, Spain..
    Tosti, G.
    Univ Perugia, Dipartimento Fis, I-06123 Perugia, Italy..
    Valverde, J.
    CNRS IN2P3, Ecole Polytech, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Vogel, M.
    Calif State Univ Los Angeles, Dept Phys & Astron, Los Angeles, CA 90032 USA..
    Wood, K.
    Praxis Inc, Alexandria, VA 22303 USA.;Naval Res Lab, Washington, DC 20375 USA..
    Investigating the Nature of Late-time High-energy GRB Emission through Joint Fermi/Swift Observations2018Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 863, nr 2, artikkel-id 138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use joint observations by the Swift X-ray Telescope (XRT) and the Fermi Large Area Telescope (LAT) of gamma-ray burst (GRB) afterglows to investigate the nature of the long-lived high-energy emission observed by Fermi LAT. Joint broadband spectral modeling of XRT and LAT data reveals that LAT nondetections of bright X-ray afterglows are consistent with a cooling break in the inferred electron synchrotron spectrum below the LAT and/or XRT energy ranges. Such a break is sufficient to suppress the high-energy emission so as to be below the LAT detection threshold. By contrast, LAT-detected bursts are best fit by a synchrotron spectrum with a cooling break that lies either between or above the XRT and LAT energy ranges. We speculate that the primary difference between GRBs with LAT afterglow detections and the nondetected population may be in the type of circumstellar environment in which these bursts occur, with late-time LAT detections preferentially selecting GRBs that occur in low wind-like circumburst density profiles. Furthermore, we find no evidence of high-energy emission in the LAT-detected population significantly in excess of the flux expected from the electron synchrotron spectrum fit to the observed X-ray emission. The lack of excess emission at high energies could be due to a shocked external medium in which the energy density in the magnetic field is stronger than or comparable to that of the relativistic electrons behind the shock, precluding the production of a dominant synchrotron self-Compton (SSC) component in the LAT energy range. Alternatively, the peak of the SSC emission could be beyond the 0.1-100 GeV energy range considered for this analysis.

  • 212.
    Akhmedov, Evgeny Kh
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Neutrino oscillations: Theory and phenomenology2006Inngår i: NEUTRINO - Proc. Int. Conf. Neutrino Phys. Astrophys., 2006, s. 16-22Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A brief overview of selected topics in the theory and phenomenology of neutrino oscillations is given. These include: oscillations in vacuum and in matter; phenomenology of 3-flavour neutrino oscillations; CP and T violation in neutrino oscillations in vacuum and in matter; matter effects on νμ ↔ ντ oscillations; parametric resonance in neutrino oscillations inside the earth; oscillations below and above the MSW resonance; unsettled issues in the theory of neutrino oscillations.

  • 213. Akrami, Yashar
    et al.
    Hassan, S. F.
    Koennig, Frank
    Schmidt-May, Angnis
    Solomon, Adam R.
    Bimetric gravity is cosmologically viable2015Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, s. 37-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bimetric theory describes gravitational interactions in the presence of an extra spin-2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, M-f, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin-2 interaction scale. This provides a late-time expansion history which is extremely close to Lambda CDM, but with a technically-natural value for the cosmological constant. We find M-f should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales. (C) 2015 The Authors. Published by Elsevier B.V.

  • 214. Akrami, Yashar
    et al.
    Koivisto, Tomi S.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Solomon, Adam R.
    The nature of spacetime in bigravity: Two metrics or none?2015Inngår i: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 47, nr 1, s. 1838-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility of matter coupling to two metrics at once is considered. This appears natural in the most general ghost-free, bimetric theory of gravity, where it unlocks an additional symmetry with respect to the exchange of the metrics. This double coupling, however, raises the problem of identifying the observables of the theory. It is shown that if the two metrics couple minimally to matter, then there is no physical metric to which all matter would universally couple, and that moreover such an effective metric generically does not exist even for an individual matter species. By studying point particle dynamics, a resolution is suggested in the context of Finsler geometry.

  • 215.
    Alday, Juan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Roth, Lorenz
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Retherford, Kurt D.
    Becker, Tracy M.
    Molyneux, Philippa
    Saur, Joachim
    New constraints on Ganymede's hydrogen corona: Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 20142017Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 148, s. 35-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.

  • 216. ALFVEN, H
    et al.
    AXNAS, I
    BRENNING, N
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    VOYAGER SATURNIAN RING MEASUREMENTS AND THE EARLY HISTORY OF THE SOLAR-SYSTEM1986Inngår i: PLANETARY AND SPACE SCIENCE, ISSN 0032-0633, Vol. 34, nr 2, s. 145-154Artikkel i tidsskrift (Fagfellevurdert)
  • 217.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    Annihilation Model of the QSOs1979Rapport (Annet vitenskapelig)
  • 218.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    Double Radio Sources and the New Approach to Cosmic Plasma Physics1977Rapport (Annet vitenskapelig)
  • 219.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    Has the Universe an Origin?1988Rapport (Annet vitenskapelig)
  • 220.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    Hubble Expansion in a Euclidean Framework1979Rapport (Annet vitenskapelig)
  • 221.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    On Hierarchical Cosmology1982Rapport (Annet vitenskapelig)
  • 222.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    Paradigm Transition in Cosmic Plasma Physics1982Rapport (Annet vitenskapelig)
  • 223.
    Alfvén, Hannes
    KTH, Tidigare Institutioner.
    Rymdforskningen och vår världsbild1982Rapport (Annet vitenskapelig)
  • 224.
    Alfvén, Hannes
    et al.
    KTH, Tidigare Institutioner.
    Arrhenius, Gustaf
    Cosmogonic Scenario1985Rapport (Annet vitenskapelig)
  • 225.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Li, Bin
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Statistical altitude distribution of the auroral density cavity2015Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 2, s. 996-1006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The statistical altitude distribution of auroral density cavities located between 3.0 and 6.5 R-E is investigated using in situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R-E. Above 6.125 R-E, none of the events exhibit precipitating inverted V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R-E the pseudo altitude increases by 0.20 per R-E, consistent with a distributed parallel electric field. Between 4.375 and 5.625 R-E the pseudo altitude increases weakly, by 0.01 per R-E, due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R-E the pseudo altitude increases by 0.28 per R-E, due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

  • 226.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    In situ observations of density cavities extending above the auroral acceleration region2014Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, nr 7, s. 5286-5294Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The uppermost part of a stable potential structure in the auroral acceleration region was studied using simultaneous observations of Cluster satellites C1 and C3. Both satellites observe a monotonically decreasing electron density as they ascend through the auroral acceleration region. As C1 exits the top of the auroral acceleration region, the electron densities continue to decrease, and the minimum electron density is reached 14 km above the upper edge of the auroral acceleration region. The electron density does not return to noncavity values until the spacecraft exits the potential structure's flux tube. The data indicate that the auroral density cavity is not confined by the potential structure and may extend above the auroral acceleration region.

  • 227.
    Alp, Dennis
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Core-collapse Supernovae: Theory vs. Observations2019Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A core-collapse supernova (CCSN) is an astronomical explosion that indicates the death of a massive star. The iron core of the star collapses into either a neutron star or a black hole while the rest of the material is expelled at high velocities. Supernovae (SNe) are important for the chemical evolution of the Universe because a large fraction of the heavier elements such as oxygen, silicon, and iron are liberated by CCSN explosions. Another important role of SNe is that the ejected material seed the next generation of stars and planets. From observations, it is clear that a large fraction of all massive stars undergoes SN explosions, but describing how SNe explode has remained a challenge for many decades.

    The attached papers focus on comparing theoretical predictions with observations, primarily observations of SN 1987A. The compact remnant in SN 1987A has not yet been detected and we have investigated how a compact object can remain hidden in the ejecta (Paper I and II). Because of the high opacity of the metal-rich ejecta, the direct X-ray observations are not very constraining even for potentially favorable viewing angles. However, the combined observations still strongly constrain fallback accretion and put a limit on possible pulsar wind activity. The thermal surface emission from a neutron star is consistent with the observations if our line of sight is dust-obscured, and only marginally consistent otherwise. Future observations provide promising opportunities for detecting the compact object.

    We have also compared the most recent three-dimensional neutrino-driven SN models that are based on explosion simulations with early X-ray and gamma-ray observations of SN 1987A (Paper III). The models that are designed to match SN 1987A fit the data well, but not all tensions can be explained by choosing a suitable viewing angle. More generally, the asymmetries do not affect the early emission qualitatively and different progenitors of the same class result in similar early emission. We also find that the progenitor metallicity is important for the low-energy X-ray cuto↵. Current instruments should be able to detect this emission from SNe at distances of 3–10 Mpc, which correspond to distances slightly beyond the Local Group.

  • 228.
    Alp, Dennis
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Early X-Ray and Gamma-Ray Emission from 3D Neutrino-Driven SN Simulations and Comparisons With Observations of SN 1987AManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    During the first few hundred days, core-collapse supernovae (CCSNe) strongly emit X-rays and gamma-rays originating from radioactive elements, primarily the 56Ni chain. We use SN models based on three-dimensional (3D) neutrino-driven explosion simulations to compute this early emission and compare the predictions to observations of SN 1987A. The agreement between the models and observations is good but small differences that cannot be matched by a suitable choice of viewing angle are evident. The discrepancies indicate that the models need to be slightly more mixed and the bulk of the 56Ni should be moving away from us at higher velocities than can be found in the models. Asymmetries and 3D structures vary the flux by a factor of a few but do not affect the emission qualitatively. The emission also shows similar properties for qualitatively similar progenitors. The only major difference is that stripped-envelope SNe evolve faster and are more than an order of magnitude more luminous. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor. Future NuSTAR observations should detect the down-scattered continuum and low-energy cutoff of (non-)stripped SNe at distances of (3)10 Mpc. INTEGRAL/SPI can detect the direct line emission at distances of (0.2)2 Mpc.

  • 229.
    Alp, Dennis
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Demory, B-O
    Refraction in exoplanet atmospheres Photometric signatures, implications for transmission spectroscopy, and search in Kepler data2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 609, artikkel-id A90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Refraction deflects photons that pass through atmospheres, which affects transit light curves. Refraction thus provides an avenue to probe physical properties of exoplanet atmospheres and to constrain the presence of clouds and hazes. In addition, an effective surface can be imposed by refraction, thereby limiting the pressure levels probed by transmission spectroscopy. Aims. The main objective of the paper is to model the effects of refraction on photometric light curves for realistic planets and to explore the dependencies on atmospheric physical parameters. We also explore under which circumstances transmission spectra are significantly affected by refraction. Finally, we search for refraction signatures in photometric residuals in Kepler data. Methods. We use the model of Hui & Seager (2002, ApJ, 572, 540) to compute deflection angles and refraction transit light curves, allowing us to explore the parameter space of atmospheric properties. The observational search is performed by stacking large samples of transit light curves from Kepler. Results. We find that out-of-transit refraction shoulders are the most easily observable features, which can reach peak amplitudes of similar to 10 parts per million (ppm) for planets around Sun-like stars. More typical amplitudes are a few ppm or less for Jovians and at the sub-ppm level for super-Earths. In-transit, ingress, and egress refraction features are challenging to detect because of the short timescales and degeneracies with other transit model parameters. Interestingly, the signal-to-noise ratio of any refraction residuals for planets orbiting Sun-like hosts are expected to be similar for planets orbiting red dwarfs and ultra-cool stars. We also find that the maximum depth probed by transmission spectroscopy is not limited by refraction for weakly lensing planets, but that the incidence of refraction can vary significantly for strongly lensing planets. We find no signs of refraction features in the stacked Kepler light curves, which is in agreement with our model predictions.

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    Amati, L.
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    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
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    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Gotz, D.
    Univ Paris Saclay, IRFU, CEA, Dept Astrophys, F-91191 Gif Sur Yvette, France..
    Bozzo, E.
    Univ Geneva, Dept Astron, Ch Ecogia 16, CH-1290 Versoix, Switzerland..
    Tenzer, C.
    Eberhard Karls Univ Tubingen, Inst Astron & Astrophys, Kepler Ctr Astro & Particle Phys, Abt Hochenergieastrophys, Sand 1, D-72076 Tubingen, Germany..
    Frontera, F.
    Univ Ferrara, Dept Phys & Earth Sci, Via Saragat 1, I-44122 Ferrara, Italy.;INAF IASF, Via Gobetti 101, I-40129 Bologna, Italy..
    Ghirlanda, G.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Labanti, C.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Osborne, J. P.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Stratta, G.
    Univ Urbino Carlo Bo, I-61029 Urbino, Italy..
    Tanvir, N.
    Univ Leicester, Dept Phys & Astron, Univ Rd, Leicester LE1 7RH, Leics, England.;Univ Leicester, Leicester Inst Space & Earth Observat, Univ Rd, Leicester LE1 7RH, Leics, England..
    Willingale, R.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Attina, P.
    GP Adv Projects, Gussago, Italy..
    Campana, R.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Castro-Tirado, A. J.
    CSIC, IAA, POB 03004, E-18080 Granada, Spain..
    Contini, C.
    OHB Italia, Via Gallarate 150, I-20151 Milan, Italy..
    Fuschino, F.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Gomboc, A.
    Univ Nova Gorica, Ctr Astrophys & Cosmol, Vipayska 11c, Ajdov V Sv cina 5270, Slovenia..
    Hudec, R.
    Czech Tech Univ, Fac Elect Engn, Prague 16627, Czech Republic.;Kazan Fed Univ, Kazan 420008, Russia..
    Orleanski, P.
    Polish Acad Sci, Space Res Ctr, Warsaw, Poland..
    Renotte, E.
    Ctr Spatial Liege, Parc Sci Sart Tilman Ave Pre Aily, B-4031 Angleur Liege, Belgium..
    Rodic, T.
    Slovenian Ctr Excellence Space Sci & Technol, SPACE SI, Ljubljana, Slovenia..
    Bagoly, Z.
    Eotv Os Univ, Budapest, Hungary..
    Blain, A.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Callanan, P.
    Univ Coll Cork, Dept Phys, Cork, Ireland..
    Covino, S.
    Brera Astron Observ, INAF, Via Bianchi 46, I-23807 Merate, LC, Italy..
    Ferrara, A.
    Scuola Normale Super Pisa, Piazza Cavalieri 7, I-56126 Pisa, Italy.;Univ Tokyo, Kavli IPMU, 5-1-5 Kashiwanoha, Kashiwa, Chiba 2778583, Japan..
    Le Floch, E.
    Univ Paris Saclay, IRFU, CEA, Dept Astrophys, F-91191 Gif Sur Yvette, France..
    Marisaldi, M.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Mereghetti, S.
    IASF Milano, INAF, Via E Bassini 15, I-20133 Milan, Italy..
    Rosati, P.
    Univ Ferrara, Via Saragat 1, Ferrara, Italy..
    Vacchi, A.
    INFN Trieste, Via Valerio 2, Trieste, Italy..
    D'Avanzo, P.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Giommi, P.
    Italian Space Agcy, ASI, Via Politecn Snc, I-00133 Rome, Italy..
    Piranomonte, S.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy..
    Piro, L.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Reglero, V
    Univ Valencia, Image Proc Lab, C Catedrat Jose Beltran 2, Valencia 46980, Spain..
    Rossi, A.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Santangelo, A.
    Eberhard Karls Univ Tubingen, Inst Astron & Astrophys, Kepler Ctr Astro & Particle Phys, Abt Hochenergieastrophys, Sand 1, D-72076 Tubingen, Germany..
    Salvaterra, R.
    Ist Astrofis Spaziale & Fis Cosm Milano, INAF, Via E Bassini 15, I-20133 Milan, Italy..
    Tagliaferri, G.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Vergani, S.
    PSL Res Univ, Observ Paris, CNRS, GEPI, Pl Jules Janssen, F-92190 Meudon, France.;Osserv Astron Brera, INAF, Via Bianchi 46, I-23807 Merate, LC, Italy..
    Vinciguerra, S.
    Univ Birmingham, Inst Gravitat Wave Astron, Birmingham B15 2TT, W Midlands, England.;Univ Birmingham, Sch Phys & Astron, Birmingham B15 2TT, W Midlands, England..
    Briggs, M.
    Univ Alabama, Ctr Space Plasma & Aeron Res, 320 Sparkman Dr, Huntsville, AL 35805 USA..
    Campolongo, E.
    OHB Italia, Via Gallarate 150, I-20151 Milan, Italy..
    Ciolfi, R.
    Osserv Astron Padova, INAF, Vicolo Osservatorio 5, I-35122 Padua, Italy.;Trento Inst Fundamental Phys & Applicat, INFN TIFPA, Via Sommarive 14, I-38123 Trento, Italy..
    Connaughton, V
    Univ Space Res Assoc, NSSTC, 320 Sparkman Dr, Huntsville, AL 35805 USA..
    Cordier, B.
    Univ Paris Saclay, IRFU, CEA, Dept Astrophys, F-91191 Gif Sur Yvette, France..
    Morelli, B.
    OHB Italia, Via Gallarate 150, I-20151 Milan, Italy..
    Orlandini, M.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Adami, C.
    Aix Marseille Univ, LAM, CNRS, F-13388 Marseille, France..
    Argan, A.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Atteia, J-L
    Univ Toulouse, UPS, CNRS, CNES,IRAP, Toulouse, France..
    Auricchio, N.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Balazs, L.
    MTA CSFK Konkoly Observ, Konkoly Thege Mut 13-17, H-1121 Budapest, Hungary..
    Baldazzi, G.
    INFN, Sez Bologna, Viale Berti Pichat 6-2, I-40127 Bologna, Italy.;Univ Bologna, Dept Phys, Viale Berti Pichat 6-2, I-40127 Bologna, Italy..
    Basa, S.
    Aix Marseille Univ, LAM, CNRS, F-13388 Marseille, France..
    Basak, Rupal
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.
    Bellutti, P.
    FBK, Via Sommarive 18, I-38123 Povo, Trento, Italy..
    Bernardini, M. G.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Bertuccio, G.
    Politecn Milan, Via Anzani 42, I-22100 Como, Italy.;INFN Milano, Via Celoria 16, I-20133 Milan, Italy..
    Braga, J.
    INPE, Av Astronautas 1758, BR-12227010 Sao Jose Dos Campos, SP, Brazil..
    Branchesi, M.
    Univ Urbino Carlo Bo, Via A Saffi 2, I-61029 Urbino, Italy.;INFN, Sez Firenze, Via G Sansone 1, I-50019 Sesto Fiorentino, Italy..
    Brandt, S.
    DTU Space Natl Space Inst Elektrovej, Bldg 327, DK-2800 Lyngby, Denmark..
    Brocato, E.
    INAF Astron Teramo, I-64100 Teramo, Italy..
    Budtz-Jorgensen, C.
    DTU Space Natl Space Inst Elektrovej, Bldg 327, DK-2800 Lyngby, Denmark..
    Bulgarelli, A.
    IASF Bologna, INAF, Via Gobetti 101, I-40129 Bologna, Italy..
    Burderi, L.
    Univ Cagliari, Dipartimento Fis, SP Monserrato Sestu Km 0-7, I-09042 Monserrato, Italy..
    Camp, J.
    Goddard Space Flight Ctr, Astrophys Sci Div, Greenbelt, MD 20771 USA..
    Capozziello, S.
    Univ Napoli Federico II, Dipartimento Fis, Via Cinthia, I-80126 Naples, Italy..
    Caruana, J.
    Univ Malta, Dept Phys, Msida 2080, Msd, Malta.;Univ Malta, Inst Space Sci & Astron, Msida 2080, Msd, Malta..
    Casella, P.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy..
    Cenko, B.
    NASA, Goddard Space Flight Ctr, Astrophys Sci Div, Mail Code 661, Greenbelt, MD 20771 USA.;Univ Maryland, Joint Space Sci Inst, College Pk, MD 20742 USA..
    Chardonnet, P.
    Univ Savoie, CNRS, LAPTh, BP 110, F-74941 Annecy Le Vieux, France.;Natl Res Nucl Univ MEPhI, 31 Kashirskoe Sh, Moscow 115409, Russia..
    Ciardi, B.
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85741 Garching, Germany..
    Colafrancesco, S.
    Univ Witwatersrand, Sch Phys, Private Bag 3, ZA-2050 Johannesburg, South Africa..
    Dainotti, M. G.
    Stanford Univ, Dept Phys & Astron, Via Pueblo Mall 382, Stanford, CA 94305 USA.;INAF OAS Bologna, Via P Gobetti 93-3, Bologna, Italy.;Uniwersytet Jagiellonski, Obserwatorium Astron, Ul Orla 171, PL-31501 Krakow, Poland..
    D'Elia, V
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy.;Agenzia Spaziale Italiana, SSDC, Via Politecn Snc, I-00133 Rome, Italy..
    De Martino, D.
    Capodimonte Astron Observ Naples, INAF, Via Moiariello 16, I-80131 Naples, Italy..
    De Pasquale, M.
    Istanbul Univ, Dept Astron & Space Sci, TR-34119 Istanbul, Turkey..
    Del Monte, E.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Della Valle, M.
    Osserv Astron Capodimonte, INAF, Salita Moiariello 16, I-80131 Naples, Italy.;Int Ctr Relativist Astrophys, Piazzale Repubbl 2, I-65122 Pescara, Italy..
    Drago, A.
    INFN, Via Enrico Fermi 40, Frascati, Italy..
    Evangelista, Y.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Feroci, M.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Finelli, F.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Fiorini, M.
    Ist Astrofis Spaziale & Fis Cosm Milano, INAF, Via E Bassini 15, I-20133 Milan, Italy..
    Fynbo, J.
    Univ Copenhagen, Dark Cosmol Ctr, Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark..
    Gal-Yam, A.
    Weizmann Inst Sci, Fac Phys, Dept Particle Phys & Astrophys, IL-76100 Rehovot, Israel..
    Gendre, B.
    Univ Virgin Isl, 2 John Brewers Bay, St Thomas, VI 00802 USA.;Etelman Observ, Bonne Resolut, St Thomas, VI USA..
    Ghisellini, G.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Grado, A.
    Capodimonte Astron Observ Naples, INAF, Via Moiariello 16, I-80131 Naples, Italy..
    Guidorzi, C.
    Univ Ferrara, Dept Phys & Earth Sci, Via Saragat 1, I-44122 Ferrara, Italy..
    Hafizi, M.
    Univ Tirana, Dept Phys, Tirana, Albania..
    Hanlon, L.
    Univ Coll Dublin, Sch Phys, Space Sci Grp, Dublin 4, Ireland..
    Hjorth, J.
    Univ Copenhagen, Dark Cosmol Ctr, Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark..
    Izzo, L.
    CSIC, IAA, Glorieta Astron S-N, E-18008 Granada, Spain..
    Kiss, L.
    Hungarian Acad Sci, Res Ctr Astron & Earth Sci, Konkoly Observ, Konkoly Thege Miklosut 15-17, H-1121 Budapest, Hungary..
    Kumar, P.
    Univ Texas Austin, Dept Astron, Austin, TX 78712 USA..
    Kuvvetli, I
    DTU Space Natl Space Inst Elektrovej, Bldg 327, DK-2800 Lyngby, Denmark..
    Lavagna, M.
    Politecn Milan, Via La Masa 1, I-20156 Milan, Italy..
    Li, T.
    Tsinghua Univ, Dept Engn Phys, Beijing, Peoples R China.;Tsinghua Univ, Ctr Astrophys, Beijing, Peoples R China..
    Longo, F.
    INFN Trieste, Via Valerio 2, Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, Trieste, Italy..
    Lyutikov, M.
    Purdue Univ, Dept Phys, 525 Northwestern Ave, W Lafayette, IN 47907 USA.;McGill Univ, Dept Phys, 3600 Univ St, Montreal, PQ H3A 2T8, Canada.;McGill Univ, McGill Space Inst, 3600 Univ St, Montreal, PQ H3A 2T8, Canada..
    Maio, U.
    Leibniz Inst Astrophys, Sternwarte 16, D-14482 Potsdam, Germany.;Osserv Astron Trieste, INAF, Via G Tiepolo 11, I-34131 Trieste, Italy..
    Maiorano, E.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Malcovati, P.
    Univ Pavia, Dept Elect Comp & Biomed Engn, Pavia, Italy..
    Malesani, D.
    Univ Copenhagen, Dark Cosmol Ctr, Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark..
    Margutti, R.
    Northwestern Univ, CIERA, Evanston, IL 60208 USA.;Northwestern Univ, Dept Phys & Astrophys, Evanston, IL 60208 USA..
    Martin-Carrillo, A.
    Univ Coll Dublin, Sch Phys, Space Sci Grp, Dublin 4, Ireland..
    Masetti, N.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy.;Univ Andres Bello, Dept Ciencias Fis, Fernandez Concha 700, Santiago, Chile..
    McBreen, S.
    Univ Coll Dublin, Sch Phys, Stillorgan Rd, Dublin 4, Ireland..
    Mignani, R.
    Ist Astrofis Spaziale & Fis Cosm Milano, INAF, Via E Bassini 15, I-20133 Milan, Italy.;Univ Zielona Gora, Janusz Gil Inst Astron, Lubuska 2, PL-65265 Zielona Gora, Poland..
    Morgante, G.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Mundell, C.
    Univ Bath, Dept Phys, Bath BA2 7AY, Avon, England..
    Nargaard-Nielsen, H. U.
    DTU Space Natl Space Inst Elektrovej, Bldg 327, DK-2800 Lyngby, Denmark..
    Nicastro, L.
    Inst Astrofis Spaziale & Fis Cosm, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Palazzi, E.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Paltani, S.
    Univ Geneva, Dept Astron, Ch Ecogia 16, CH-1290 Versoix, Switzerland..
    Panessa, F.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Pareschi, G.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Pe'er, A.
    Univ Coll Cork, Dept Phys, Cork, Ireland..
    Penacchioni, A. , V
    Pian, E.
    Scuola Normale Super Pisa, Piazza Cavalieri 7, I-56126 Pisa, Italy..
    Piedipalumbo, E.
    Univ Napoli Federico II, Dipartimento Fis, Compl Univ Monte S Angelo, I-80126 Naples, Italy.;INFN, Sez Napoli, Univ Monte S Angelo,Edificio 6,Via Cinthia, I-80126 Naples, Italy..
    Piran, T.
    Hebrew Univ Jerusalem, Racah Inst Phys, IL-91904 Jerusalem, Israel..
    Rauw, G.
    Univ Liege, Quartier Agora, Allee 6 Aout 19c, B-4000 Liege, Belgium..
    Razzano, M.
    Univ Pisa, Dept Phys, I-56127 Pisa, Italy.;INFN Pisa, I-56127 Pisa, Italy..
    Read, A.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Rezzolla, L.
    Goethe Univ Frankfurt, Inst Theoret Phys, Max von Laue Str 1, D-60438 Frankfurt, Germany.;Frankfurt Inst Adv Studies, Ruth Moufang Str 1, D-60438 Frankfurt, Germany..
    Romano, P.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, Italy..
    Ruffini, R.
    ICRANet, Pzza Repubbl 10, I-65122 Pescara, Italy.;Sapienza Univ Roma, ICRA, Ple Aldo Moro 5, I-00185 Rome, Italy.;Sapienza Univ Roma, Dipartimento Fis, Ple Aldo Moro 5, I-00185 Rome, Italy..
    Savaglio, S.
    Univ Calabria, Phys Dept, Via P Bucci, I-87036 Arcavacata Di Rende, Italy..
    Sguera, V
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Schady, P.
    Max Planck Inst Extraterr Phys, Giessenbachstr 1, D-85748 Garching, Germany..
    Skidmore, W.
    Thirty Meter Telescope Int Observ, 100 W Walnut St,Suite 300, Pasadena, CA 91124 USA..
    Song, L.
    Chinese Acad Sci, Inst High Energy Phys, Key Lab Particle Astrophys, Beijing 100049, Peoples R China..
    Stanway, E.
    Univ Warwick, Dept Phys, Gibbet Hill Rd, Coventry CV4 7AL, W Midlands, England..
    Starling, R.
    Univ Leicester, Dept Phys & Astron, Univ Rd, Leicester LE1 7RH, Leics, England.;Univ Leicester, Leicester Inst Space & Earth Observat, Univ Rd, Leicester LE1 7RH, Leics, England..
    Topinka, M.
    Dublin Inst Adv Studies, Sch Cosm Phys, 31 Fitzwilliam Pl, Dublin 2, Ireland..
    Troja, E.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA.;NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA..
    van Putten, M.
    Sejong Univ, 98 Gunja Dong, Seoul 143747, South Korea..
    Vanzella, E.
    Osservatorio Astron Bologna, INAF, Via Ranzani 1, I-40127 Bologna, Italy..
    Vercellone, S.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, Italy..
    Wilson-Hodge, C.
    NASA, Marshall Space Flight Ctr, Huntsville, AL USA..
    Yonetoku, D.
    Kanazawa Univ, Fac Math & Phys, Kanazawa, Ishikawa 9201192, Japan..
    Zampa, G.
    INFN Trieste, Via Valerio 2, Trieste, Italy..
    Zampa, N.
    INFN Trieste, Via Valerio 2, Trieste, Italy..
    Zhang, B.
    Univ Nevada, Dept Phys & Astron, Las Vegas, NV 89154 USA..
    Zhang, B. B.
    CSIC, IAA, POB 03004, E-18080 Granada, Spain..
    Zhang, S.
    Inst High Energy Phys, Beijing 100049, Peoples R China..
    Zhang, S-N
    Inst High Energy Phys, Beijing 100049, Peoples R China..
    Antonelli, A.
    ASDC, Via Politecn Snc, I-00133 Rome, Italy..
    Bianco, F.
    NYU, Ctr Cosmol & Particle Phys, 4 Washington Pl, New York, NY 10003 USA..
    Boci, S.
    Univ Tirana, Dept Phys, Tirana, Albania..
    Boer, M.
    Univ Cote dAzur, Observ Cote dAzur, ARTEMIS, CNRS UMR 5270,CS 34229, Blvd Observ, F-06304 Nice 04, France..
    Botticella, M. T.
    Capodimonte Astron Observ Naples, INAF, Via Moiariello 16, I-80131 Naples, Italy..
    Boulade, O.
    Univ Paris Saclay, IRFU, CEA, Dept Astrophys, F-91191 Gif Sur Yvette, France..
    Butler, C.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    Campana, S.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Capitanio, F.
    IAPS Roma, INAF, Via Fosso Cavaliere 100, I-00133 Rome, Italy..
    Celotti, A.
    Osserv Astron Brera, INAF, Via Bianchi 46, I-23807 Merate, LC, Italy.;SISSA, Via Bonomea 265, I-34136 Trieste, Italy.;INFN, Sez Trieste, Via Valerio 2, I-34127 Trieste, Italy..
    Chen, Y.
    Inst High Energy Phys, Beijing 100049, Peoples R China..
    Colpi, M.
    Univ Milano Bicocca, Dipartimento Fis G Occhialini, Piazza Sci 3, I-20126 Milan, Italy.;INFN, Sez Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Comastri, A.
    Osservatorio Astron Bologna, INAF, Via Piero Gobetti 93-3, I-40129 Bologna, Italy..
    Cuby, J-G
    LAM, F-13388 Marseille, France..
    Dadina, M.
    IASF Bologna, INAF, via P Gobetti 101, I-40129 Bologna, Italy..
    De Luca, A.
    Ist Astrofis Spaziale & Fis Cosm Milano, INAF, Via E Bassini 15, I-20133 Milan, Italy..
    Dong, Y-W
    Inst High Energy Phys, Beijing 100049, Peoples R China..
    Ettori, S.
    INFN, Sez Bologna, Viale Berti Pichat 6-2, I-40127 Bologna, Italy.;Osservatorio Astron Bologna, INAF, Via Piero Gobetti 93-3, I-40129 Bologna, Italy..
    Gandhi, P.
    Univ Southampton, Dept Phys & Astron, Southampton SO17 1BJ, Hants, England..
    Geza, E.
    Hungarian Acad Sci, Wigner Res Ctr Phys, POB 49, H-1525 Budapest, Hungary..
    Greiner, J.
    Max Planck Inst Astrophys, Karl Schwarzschild Str 1, D-85741 Garching, Germany..
    Guiriec, S.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA.;George Washington Univ, Dept Phys, 725 21st St NW, Washington, DC 20052 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;CRESST, Greenbelt, MD 20771 USA..
    Harms, J.
    Univ Urbino Carlo Bo, I-61029 Urbino, Italy..
    Hernanz, M.
    CSIC, Inst Space Sci IEEC, Carrer Can Magrans S-N, E-08193 Barcelona, Spain..
    Hornstrup, A.
    DTU Space Natl Space Inst Elektrovej, Bldg 327, DK-2800 Lyngby, Denmark..
    Hutchinson, I
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Israel, G.
    Osserv Astron Roma, INAF, Via Frascati 33, I-00040 Monte Porzio Catone, Italy..
    Jonker, P.
    SRON, Netherlands Inst Space Res, Sorbonnelaan 2, NL-3584 CA Utrecht, Netherlands.;Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Kaneko, Y.
    Sabanc Univ, Fac Engn & Nat Sci, TR-34956 Istanbul, Turkey..
    Kawai, N.
    Tokyo Inst Technol, Dept Phys, Meguro Ku, 2-12-1 Ookayama, Tokyo 1528551, Japan..
    Wiersema, K.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Korpela, S.
    Univ Helsinki, Dept Phys, POB 48, FIN-00014 Helsinki, Finland..
    Lebrun, V
    LAM, F-13388 Marseille, France..
    Lu, F.
    Inst High Energy Phys, Beijing 100049, Peoples R China..
    MacFadyen, A.
    NYU, Ctr Cosmol & Particle Phys, New York, NY USA..
    Malaguti, G.
    IASF Bologna, INAF, Via Piero Gobetti 101, I-40129 Bologna, Italy..
    Maraschi, L.
    Osserv Astron Brera, INAF, Via E Bianchi 46, I-23807 Merate, LC, Italy..
    Melandri, A.
    Osserv Astron Brera, INAF, Via E Bianchi 36, I-23807 Merate, LC, Italy..
    Modjaz, M.
    NYU, Ctr Cosmol & Particle Phys, Dept Phys, 726 Broadway Off 1044, New York, NY 10003 USA..
    Morris, D.
    Etelman Observ, St Thomas, VI 00802 USA.;Univ Virgin Isl, Coll Sci & Math, St Thomas, VI 00802 USA..
    Omodei, N.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, WW Hansen Expt Phys Lab, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Paizis, A.
    IASF Milano, INAF, Via E Bassini 15, I-20133 Milan, Italy..
    Pata, P.
    Czech Tech Univ, Fac Elect Engn, Dept Radioelect, Tech 2, Prague 16627 6, Czech Republic..
    Petrosian, V
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, WW Hansen Expt Phys Lab, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Rachevski, A.
    INFN, Sez Trieste, Via Valerio 2, I-34127 Trieste, Italy..
    Rhoads, J.
    Arizona State Univ, Sch Earth & Space Explorat, Tempe, AZ 85287 USA.;Goddard Space Flight Ctr, Astrophys Sci Div, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA..
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.
    Sabau-Graziati, L.
    INTA, Div Ciencias Espacio, Madrid, Spain..
    Shigehiro, N.
    RIKEN, ABBL, Wako, Saitama 3510198, Japan..
    Sims, M.
    Univ Leicester, Dept Phys & Astron, Leicester LE1 7RH, Leics, England..
    Soomin, J.
    CSIC, IAA, Glorieta Astron S-N, E-18008 Granada, Spain..
    Szecsi, D.
    Univ Birmingham, Inst Gravitat Wave Astron, Birmingham B15 2TT, W Midlands, England.;Univ Birmingham, Sch Phys & Astron, Birmingham B15 2TT, W Midlands, England.;Czech Acad Sci, Astron Inst, Frivcova 298, Ondvrejov 25165, Czech Republic..
    Urata, Y.
    Natl Cent Univ, Inst Astron, Chungli 32054, Taiwan..
    Uslenghi, M.
    IASF Bologna, INAF, Via E Bassini 15, I-20133 Milan, Italy..
    Valenziano, L.
    IASF Bologna, INAF, Via Gobetti 101, Bologna, Italy..
    Vianello, G.
    Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Vojtech, S.
    Acad Sci Czech Republ, Astron Inst, Fricova 1, CZ-25165 Ondrejov, Czech Republic..
    Watson, D.
    Univ Copenhagen, Dark Cosmol Ctr, Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark..
    Zicha, J.
    Czech Tech Univ, Fac Mech Engn, Dept Instrumentat & Control Engn, Tech 4, Prague 16607 6, Czech Republic..
    The THESEUS space mission concept: science case, design and expected performances2018Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, nr 1, s. 191-244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRB and X-ray transient detection over a broad field of view (more than 1 sr) with 0.5-1 arcmin localization, an energy band extending from several MeV down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift similar to 10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late '20s/early '30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).

  • 231.
    Andersson, Karl E.
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Madejski, G M
    Complex structure of galaxy cluster A1689: Evidence for a merger from X-ray data?2004Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 607, nr 1, s. 190-201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A1689 is a galaxy cluster at z = 0.183 for which previous measurements of its mass by using various techniques gave discrepant results. We present a new detailed measurement of the mass with the data based on X-ray observations with the European Photon Imaging Camera aboard the XMM-Newton Observatory, determined by using an unparameterized deprojection technique. Fitting the total mass profile to a Navarro-Frenk-White model yields halo concentration c = 7.2(-2.4)(+1.6) and r(200) = 1.13 +/- 0.21 h(-1) Mpc, corresponding to a mass that is less than half of that found from gravitational lensing. Adding to the evidence of substructure from optical observations, X-ray analysis shows a highly asymmetric temperature profile and a nonuniform redshift distribution, implying large-scale relative motion of the gas. A lower than expected gas mass fraction f(gas) = 0.072 +/- 0: 008 (for a flat LambdaCDM cosmology) suggests a complex spatial and/or dynamical structure. We also find no sign of any additional absorbing component previously reported on the basis of the Chandra data, confirming the XMM-Newton low-energy response by using data from ROSAT.

  • 232. Andersson, V.
    et al.
    Chen, P.
    Kamae, T.
    Madejski, G.
    Mizuno, T.
    Ng, J. S. T.
    Suhonen, M.
    Tajima, H.
    Thurston, T.
    Bogaert, G.
    Fukazawa, Y.
    Saito, Y.
    Takahashi, T.
    Barbier, L.
    Bloser, P.
    Cline, T.
    Harding, A.
    Hunter, S.
    Krizmanic, J.
    Mitchell, J.
    Streitmatter, R.
    Fernholz, R.
    Groth, E.
    Marlow, D.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Klamra, Wlodzimierz
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Bjornsson, C. -I
    Fransson, C.
    Larsson, S.
    Ryde, Felix
    Stockholm University.
    Arimoto, M.
    Ikagawa, T.
    Kanai, Y.
    Kataoka, J.
    Kawai, N.
    Yatsu, Y.
    Gunji, S.
    Sakurai, H.
    Yamashita, Y.
    Large-Area Balloon-Borne Polarized Gamma Ray Observer (PoGO)2005Inngår i: Proceedings of the 22nd Texas Symposium on Relativistic Astrophysics at Stanford, 2005, s. 736-743Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We are developing a new balloon-borne instrument (PoGO), to measure polarization of soft gamma rays (30-200 keV) using asymmetry in azimuth angle distribution of Compton scattering. PoGO is designed to detect 10 % polarization in 100mCrab sources in a 6-8 hour observation and bring a new dimension to studies on gamma ray emission/transportation mechanism in pulsars, AGNs, black hole binaries, and neutron star surface. The concept is an adaptation to polarization measurements of well-type phoswich counter consisting of a fast plastic scintillator (the detection part), a slow plastic scintillator (the active collimator) and a BGO scintillator (the bottom anti-counter). PoGO consists of close-packed array of 217 hexagonal well-type phoswich counters and has a narrow field-of-view (~ 5 deg2) to reduce possible source confusion. A prototype instrument has been tested in the polarized soft gamma-ray beams at Advanced Photon Source (ANL) and at Photon Factory (KEK). On the results, the polarization dependence of EGS4 has been validated and that of Geant4 has been corrected.

  • 233. Andre, M.
    et al.
    Behlke, R.
    Wahlund, J. E.
    Vaivads, A.
    Eriksson, A. I.
    Tjulin, A.
    Carozzi, T. D.
    Cully, C.
    Gustafsson, G.
    Sundkvist, D.
    Khotyaintsev, Y.
    Cornilleau-Wehrlin, N.
    Rezeau, L.
    Maksimovic, M.
    Lucek, E.
    Balogh, A.
    Dunlop, M.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Mozer, F.
    Pedersen, A.
    Fazakerley, A.
    Multi-spacecraft observations of broadband waves near the lower hybrid frequency at the Earthward edge of the magnetopause2001Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, nr 12-okt, s. 1471-1481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Broadband waves around the lower hybrid frequency (around 10 Hz) near the magnetopause are studied, using the four Cluster satellites. These waves are common at the Earthward edge of the boundary layer, consistent with earlier observations, and can have amplitudes at least up to 5 mV/m. These waves are similar on all four Cluster satellites, i.e. they are likely to be distributed over large areas of the boundary. The strongest electric fields occur during a few seconds, i.e. over distances of a few hundred km in the frame of the moving magnetopause, a scale length comparable to the ion gyroradius. The strongest magnetic oscillations in the same frequency range are typically found in the boundary layer, and across the magnetopause. During an event studied in detail, the magnetopause velocity is consistent with a large-scale depression wave, i.e. an inward bulge of magnetosheath plasma, moving tailward along the nominal magnetopause boundary. Preliminary investigations indicate that a rather flat front side of the large-scale wave is associated with a rather static small-scale electric field, while a more turbulent backside of the large-scale wave is associated with small-scale time varying electric field wave packets.

  • 234. Andrievsky, Alexander
    et al.
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Department of Astronomy, Stockholm University, AlbaNova University Center, Stockholm, Sweden.
    Noullez, Alain
    Zheligovsky, Vladislav
    Negative magnetic eddy diffusivities from the test-field method and multiscale stability theory2015Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 811, nr 2, artikkel-id 135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The generation of a large-scale magnetic field in the kinematic regime in the absence of an alpha-effect is investigated by following two different approaches: the test-field method and the multiscale stability theory relying on the homogenization technique. Our computations of the magnetic eddy diffusivity tensor of the parity-invariant flow IV of G. O. Roberts and the modified Taylor-Green flow confirm the findings of previous studies. and also explain some of their apparent contradictions. The two flows have large symmetry groups; this is used to considerably simplify the eddy diffusivity tensor. Finally, a new analytic result is presented: upon expressing the eddy diffusivity tensor in terms of solutions to auxiliary problems for the adjoint operator, we derive relations between the magnetic eddy diffusivity tensors that arise for mutually reverse small-scale flows v(x) and - v(x).

  • 235. Antipin, Oleg
    et al.
    Mojaza, Matin
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Sannino, Francesco
    Minimal Coleman-Weinberg theory explains the diphoton excess2016Inngår i: PHYSICAL REVIEW D, ISSN 2470-0010, Vol. 93, nr 11, artikkel-id 115007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We replace the standard Higgs-mechanism by the Coleman-Weinberg mechanism, and investigate its viability through the addition of a new scalar field. As we showed in a previous study, minimal models of this type can alleviate the hierarchy problem of the Higgs-mass through the so-called Veltman conditions. We here extend the previous analysis by taking into account the important difference between running mass and pole mass of the scalar states. We then investigate whether these theories can account for the 750 GeV excess in diphotons observed by the LHC collaborations. New QCD-colored fermions in the TeV mass range coupled to the new scalar state are needed to describe the excess. We further show, by explicit computation of the running of the couplings, that the model is under perturbative control till just above the masses of the heaviest states of the theory. We further suggest related testable signatures and thereby show that the LHC experiments can test these models.

  • 236. Apostolakis, A
    et al.
    Aslanides, E.
    -.
    Backenstoss, G.
    -.
    Bargassa, P.
    -.
    Behnke, O.
    -.
    Benelli, A.
    -.
    Bertin, V.
    -.
    Blanc, F.
    -.
    Bloch, P.
    -.
    Carlson, P.
    KTH, Skolan för teknikvetenskap (SCI).
    Danielsson, Mats
    KTH, Tidigare Institutioner, Fysik.
    A determination of the CP violation parameter η+- from the decay of strangeness-tagged neutral kaons1999Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 458, nr 4, s. 545-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.

  • 237. Arimoto, Makoto
    et al.
    Asano, Katsuaki
    Ohno, Masanori
    Veres, Peter
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik. Tokyo Metropolitan University, Japan.
    Bissaldi, Elisabetta
    Tachibana, Yutaro
    Kawai, Nobuyuki
    HIGH-ENERGY NON-THERMAL AND THERMAL EMISSION FROM GRB 141207A DETECTED BY FERMI2016Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 833, nr 2, artikkel-id 139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A bright long gamma-ray burst GRB 141207A was observed by the Fermi Gamma-ray Space Telescope and detected by both instruments onboard. The observations show that the spectrum in the prompt phase is not well described by the canonical empirical Band function alone, and that an additional power-law component is needed. In the early phase of the prompt emission, a modified blackbody with a hard low-energy photon index (alpha = +0.2 to +0.4) is detected, which suggests a photospheric origin. In a finely time-resolved analysis, the spectra are also well fitted by the modified blackbody combined with a power-law function. We discuss the physical parameters of the photosphere such as the bulk Lorentz factor of the relativistic flow and the radius. We also discuss the physical origin of the extra power-law component observed during the prompt phase in the context of different models such as leptonic and hadronic scenarios in the internal shock regime and synchrotron emission in the external forward shock. In the afterglow phase, the temporal and spectral behaviors of the temporally extended high-energy emission and the fading X-ray emission detected by the X-Ray Telescope on-board Swift are consistent with synchrotron emission in a radiative external forward shock.

  • 238. Atwood, W. B.
    et al.
    Abdo, A. A.
    Ackermann, M.
    Althouse, W.
    Johnson, A. S.
    Klamra, Wlodzimierz
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pearce, Mark
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Ryde, Felix
    Ziegler, M.
    Carlson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Conrad, Jan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Hjalmarsdotter, Linnea
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Moretti, Elena
    University and INFN of Trieste.
    THE LARGE AREA TELESCOPE ON THE FERMI GAMMA-RAY SPACE TELESCOPE MISSION2009Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 697, nr 2, s. 1071-1102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Large Area Telescope (Fermi/LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view (FoV), high-energy gamma-ray telescope, covering the energy range from below 20 MeV to more than 300 GeV. The LAT was built by an international collaboration with contributions from space agencies, high-energy particle physics institutes, and universities in France, Italy, Japan, Sweden, and the United States. This paper describes the LAT, its preflight expected performance, and summarizes the key science objectives that will be addressed. On-orbit performance will be presented in detail in a subsequent paper. The LAT is a pair-conversion telescope with a precision tracker and calorimeter, each consisting of a 4 x 4 array of 16 modules, a segmented anticoincidence detector that covers the tracker array, and a programmable trigger and data acquisition system. Each tracker module has a vertical stack of 18 (x, y) tracking planes, including two layers (x and y) of single-sided silicon strip detectors and high-Z converter material (tungsten) per tray. Every calorimeter module has 96 CsI(Tl) crystals, arranged in an eight-layer hodoscopic configuration with a total depth of 8.6 radiation lengths, giving both longitudinal and transverse information about the energy deposition pattern. The calorimeter's depth and segmentation enable the high-energy reach of the LAT and contribute significantly to background rejection. The aspect ratio of the tracker (height/width) is 0.4, allowing a large FoV (2.4 sr) and ensuring that most pair-conversion showers initiated in the tracker will pass into the calorimeter for energy measurement. Data obtained with the LAT are intended to (1) permit rapid notification of high-energy gamma-ray bursts and transients and facilitate monitoring of variable sources, (2) yield an extensive catalog of several thousand high-energy sources obtained from an all-sky survey, (3) measure spectra from 20 MeV to more than 50 GeV for several hundred sources, (4) localize point sources to 0.3-2 arcmin, (5) map and obtain spectra of extended sources such as SNRs, molecular clouds, and nearby galaxies, (6) measure the diffuse isotropic gamma-ray background up to TeV energies, and (7) explore the discovery space for dark matter.

  • 239.
    Axelsson, Magnus
    Department of Astronomy, Stockholm University.
    Cool Discs, Hot Flows: The Varying Faces of Accreting Compact Objects: Preface2008Inngår i: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1054, s. vii-Artikkel i tidsskrift (Annet vitenskapelig)
  • 240.
    Axelsson, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Photospheric emission from gamma-ray bursts2013Inngår i: EAS Publications Series, 2013, s. 53-57Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In spite of extensive research over the past decades, a complete physical picture of the origin of the prompt gamma-ray burst emission is still lacking. During recent years, evidence has been accumulating that the jet photosphere plays an important role. In this paper we summarize the lessons learned from Fermi observations regarding the behavior of the photosphere and discuss why photospheric emission does not necessarily appear as blackbody radiation. We concentrate on two strong and important bursts, GRB 090902B and GRB 110721A, which serve as examples of the standard appearance photospheric emission may have in gamma-ray burst spectra.

  • 241.
    Axelsson, Magnus
    Department of Astronomy, Stockholm University.
    Rapid X-ray variability in Cygnus X-l2008Inngår i: Cool Discs, Hot Flows: The Varying Faces of Accreting Compact Objects, 2008, Vol. 1054, s. 135-141Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, results from temporal analysis of RXTE observations of the black hole binary Cygnus X-l are reviewed. By tapping into the large amount of archival data available, a systematic study of the variability, in the form of the power spectrum, is conducted. It is clear that timing studies can give valuable information on the emission mechanisms and accretion geometry. Tying characteristic frequencies to effects predicted by general relativity directly gives information about the parameters of the compact object. The results show that the characteristic frequencies seen in the power spectrum follow the relation predicted for the nodal and periastron precessional frequencies of relativistic precession. From this relation, the spin of the black hole is determined to a*=0.48±0.01 for a mass of 9 M⊙. During times of high hardness, the hardness-flux correlation seen in the hard state of the source disappears on short timescales. Together with the variable characteristic frequencies, this is interpreted as support for the truncated disk scenario.

  • 242.
    Axelsson, Magnus
    et al.
    Department of Astronomy, Stockholm University.
    Borgonovo, Luis
    Department of Astronomy, Stockholm University.
    Larsson, S.
    Probing the temporal variability of Cygnus X-1 into the soft state2006Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 452, nr 3, s. 975-984Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Building on results from previous studies of Cygnus X-1, we analyze Rossi X-ray Timing Explorer (RXTE) data taken when the source was in the soft and transitional spectral states. We look at the power spectrum in the 0.01-50 Hz range, using a model consisting of a cut-off power-law and two Lorentzian components. We are able to constrain the relation between the characteristic frequencies of the Lorentzian components, and show that it is consistent with a power-law relation having the same index (1.2) as previously reported for the hard state, but shifted by a factor ∌2. Furthermore, it is shown that the change in the frequency relation seen during the transitions can be explained by invoking a shift of one Lorentzian component to a higher harmonic, and we explore the possible support for this interpretation in the other component parameters. With the improved soft state results we study the evolution of the fractional variance for each temporal component. This approach indicates that the two Lorentzian components are connected to each other, and unrelated to the power-law component in the power spectrum, pointing to at least two separate emission components.

  • 243.
    Axelsson, Magnus
    et al.
    Department of Astronomy, Stockholm University.
    Borgonovo, Luis
    Department of Astronomy, Stockholm University.
    Larsson, Stefan
    Evolution of the 0.01-25 Hz power spectral components in Cygnus X-12005Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 438, nr 3, s. 999-1012Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Analyzing the archival data from the Rossi X-ray Timing Explorer (RXTE), we study the power density spectra (PDS) of Cygnus X-1 from 1996 to 2003 in the frequency range of 0.01-25 Hz. Using a model consisting of one or two Lorentzians and/or an exponentially cut-off power-law, we are able to achieve a good fit to the PDS during the observations. With our model we are also able to track the evolution of the Lorentzian components through all spectral states of the source. We confirm the relation between characteristic frequencies seen both in black hole candidate and neutron star sources, and show the changes in this relation during the transitional and soft states of the source. The connection between the Lorentzian components is investigated by analyzing similarities and differences in their behavior. We find that the spectral state of the source can be uniquely determined from the parameters of these components. The parameter correlations can all be described by continuous functions, which differ between components. We discuss our results in the context of relativistic precession model for the accretion disk, and show a remarkable agreement between the model prediction and the data in the hard state. We estimate a value for the specific angular momentum of a* = 0.49 (-0.57) in the case of prograde (retrograde) rotation and an estimate for the inner radius of 22 to 50 (25 to 55) gravitational radii. Additional assumptions are required to explain the soft state data, and attempting to invoke rotational reversal for state transitions shows that it is insufficient to explain the differences between the hard and soft state data. © ESO 2005.

  • 244.
    Axelsson, Magnus
    et al.
    Lund Observatory, Lund University.
    Church, Ross P.
    Davies, Melvyn B.
    Levan, Andrew J.
    Ryde, Felix
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    On the origin of black hole spin in high-mass black hole binaries: Cygnus X-12011Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 412, nr 4, s. 2260-2264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To date, there have been several detections of high-mass black hole binaries in both the Milky Way and other galaxies. For some of these, the spin parameter of the black hole has been estimated. As many of these systems are quite tight, a suggested origin of the spin is angular momentum imparted by the synchronous rotation of the black hole progenitor with its binary companion. Using Cygnus X-1, the best studied high-mass black hole binary, we investigate this possibility. We find that such an origin of the spin is not likely, and our results point rather to the spin being the result of processes during the collapse.

  • 245.
    Axelsson, Magnus
    et al.
    Department of Astronomy, Stockholm University.
    Hjalmarsdotter, L.
    Borgonovo, L.
    Larsson, S.
    Vanishing hardness-flux correlation in Cygnus X-1: Signs of the disc moving out2008Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 490, nr 1, s. 253-258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. We investigate observations of the X-ray binary Cygnus X-1 with unusually high hardness and low flux. In particular, we study the characteristic frequencies seen in the PDS and the hardness-flux correlation within and between these observations.Methods. We analyse observations of Cyg X-1 during periods when the source reaches its highest hardness levels (≳ 1 for the 9-20 keV over 2-4 keV RXTE/PCA count ratios, corresponding to Γ ≲ 1.6). Using the relativistic precession model to interpret the PDS, we estimate a value for the inner radius of the accretion disc. We also study the hardness-flux correlation.Results. In the selected observations, the characteristic frequencies seen in the power spectrum are shifted to the lowest end of their frequency range. Within a single observation, the hardness-flux correlation is very weak, contrary to the negative correlation normally observed in the hard state. We suggest that this could be interpreted as the inner disc boundary being at large radii (≳50Rg), thereby requiring more time to adjust to a changing accretion rate than allowed by a single RXTE observation, and compare our findings to estimates of the viscous time scale responsible for small scale variability in the system.

  • 246.
    Axelsson, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Jackson, Miranda
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lundman, Christoffer
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Moretti, Elena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Nymark, Tanja
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Pe'Er, A.
    et al.,
    GRB110721A: An extreme peak energy and signatures of the photosphere2012Inngår i: The Astrophysical Journal. Letters, ISSN 2041-8205, Vol. 757, nr 2, s. L31-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The burst consisted of one major emission episode which lasted for ~24.5 seconds (in the GBM) and had a peak flux of 5.7\pm0.2 x 10^{-5} erg/s/cm^2. The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum. The peak energy of the Band component was initially 15\pm2 MeV, which is the highest value ever detected in a GRB. This measurement was made possible by combining GBM/BGO data with LAT Low Energy Events to achieve continuous 10--100 MeV coverage. The peak energy later decreased as a power law in time with an index of -1.89\pm0.10. The temperature of the blackbody component also decreased, starting from ~80 keV, and the decay showed a significant break after ~2 seconds. The spectrum provides strong constraints on the standard synchrotron model, indicating that alternative mechanisms may give rise to the emission at these energies.

  • 247.
    Axelsson, Magnus
    et al.
    Department of Astronomy, Stockholm University.
    Larsson, S.
    Hjalmarsdotter, L.
    The aperiodic broad-band X-ray variability of Cygnus X-32009Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 394, nr 3, s. 1544-1550Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the soft X-ray variability of Cygnus X-3. By combining data from the All-Sky Monitor and Proportional Counter Array instruments on the RXTE satellite with EXOSAT/Medium Energy (ME) detector observations, we are able to analyse the power density spectrum (PDS) of the source from 10-9 to 0.1 Hz, thus covering time-scales from seconds to years. As the data on the longer time-scales are unevenly sampled, we combine traditional power spectral techniques with simulations to analyse the variability in this range. The PDS at higher frequencies (≳10-3 Hz) are for the first time compared for all states of this source. We find that it is for all states well described by a power law, with index ∌ -2 in the soft states and a tendency for a less steep power law in the hard state. At longer time-scales, we study the effect of the state transitions on the PDS, and find that the variability below ∌10-7 Hz is dominated by the transitions. Furthermore, we find no correlation between the length of a high/soft-state episode and the time since the previous high/soft state. On intermediate time-scales, we find evidence for a break in the PDS at time-scales of the order of the orbital period. This may be interpreted as evidence for the existence of a tidal resonance in the accretion disc around the compact object, and constraining the mass ratio to M2/M1 ≲ 0.3.

  • 248.
    Axelsson, Magnus
    et al.
    Department of Astronomy, Stockholm University.
    Ryde, FelixDepartment of Astronomy, Stockholm University.
    Gamma-Ray Bursts: Prospects for Glast2007Konferanseproceedings (Annet vitenskapelig)
  • 249.
    Axelsson, Magnus
    et al.
    Department of Astronomy, Stockholm University.
    Ryde, Felix
    Department of Astronomy, Stockholm University.
    Gamma-Ray Bursts: Prospects for GLAST: Preface2007Inngår i: AIP Conference Proceedings, Stockholm, 2007, Vol. 906, s. vii-Konferansepaper (Annet vitenskapelig)
  • 250. Balazs, Csaba
    et al.
    Li, Tong
    Savage, Chris
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. University of Utah, United States.
    White, Martin
    Interpreting the Fermi-LAT gamma ray excess in the simplified framework2015Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 92, nr 12, artikkel-id 123520Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We test the plausibility of the hypothesis that the annihilation of a Majorana fermion dark matter particle via a scalar mediator explains the gamma ray excess from the Galactic center. Assuming that the mediator couples to all third generation fermions we calculate observables for dark matter abundance and scattering on nuclei, gamma, positron, and antiproton cosmic ray fluxes, radio emission from dark matter annihilation, and the effect of dark matter annihilations on the CMB. After discarding the controversial radio observation, we show that the dark matter model simultaneously fits the observed excesses in the cosmic gamma ray, the positron, and antiproton fluxes, while evading constraints from the CMB and direct detection. The experimental data are consistent with a dark matter (mediator) mass in the 10-100 (3-1000) GeV region and with weakly correlated couplings to bottom quarks and tau leptons with values of 10(-3) - 1 at the 68% credibility level.

2345678 201 - 250 of 825
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