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  • 1. Abdo, A. A.
    et al.
    Ackermann, M.
    Ajello, M.
    Atwood, W. B.
    Axelsson, M.
    Johannesson, G.
    Johnson, A. S.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ziegler, M.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Carlson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Moretti, Elena
    University and INFN of Trieste.
    Measurement of the Cosmic Ray e(+)+e(-) Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 18Article in journal (Refereed)
    Abstract [en]

    Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m(2) sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

  • 2. Abdo, A. A.
    et al.
    Ackermann, M.
    Ajello, M.
    Atwood, W. B.
    Axelsson, M.
    Johannesson, G.
    Johnson, A. S.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ziegler, M.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Mc Glynn, Sinéad
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Moretti, Elena
    University and INFN of Trieste.
    FERMI/LARGE AREA TELESCOPE BRIGHT GAMMA-RAY SOURCE LIST2009In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 183, no 1, p. 46-66Article in journal (Refereed)
    Abstract [en]

    Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the gamma-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than similar to 10 sigma) gamma-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) gamma-ray sources in the early mission data.

  • 3. Abdo, A. A.
    et al.
    Ackermann, M.
    Ajello, M.
    Atwood, W. B.
    Johannesson, G.
    Johnson, A. S.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ziegler, M.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    PULSED GAMMA-RAYS FROM PSR J2021+3651 WITH THE FERMI LARGE AREA TELESCOPE2009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 700, no 2, p. 1059-1066Article in journal (Refereed)
    Abstract [en]

    We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 +/- 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 +/- 0.004 +/- 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 +/- 3 +/- 11) x 10(-8) cm(-2) s(-1). The photon spectrum is well described by an exponentially cut-off power law of the form dF/dE = kE(-Gamma)e((-E/Ec)), where the energy E is expressed in GeV. The photon index is Gamma = 1.5 +/- 0.1 +/- 0.1 and the exponential cut-off is E-c = 2.4 +/- 0.3 +/- 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is < 10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 +/- 4 rad m(-2) but a poorly constrained magnetic geometry. Re-analysis of Chandra X-ray Observatory data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.

  • 4. Abdo, A. A.
    et al.
    Ackermann, M.
    Ajello, M.
    Axelsson, M.
    Johannesson, G.
    Johnson, A. S.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Angelakis, E.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    FERMI/LARGE AREA TELESCOPE DISCOVERY OF GAMMA-RAY EMISSION FROM A RELATIVISTIC JET IN THE NARROW-LINE QUASAR PMN J0948+00222009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, no 2, p. 976-984Article in journal (Refereed)
    Abstract [en]

    We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy. gamma-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.5846). The optical spectrum of this object exhibits rather narrow H beta (FWHM(H beta) similar to 1500 km s(-1)), weak forbidden lines, and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at a high Eddington ratio. The radio loudness and variability of the compact radio core indicate the presence of a relativistic jet. Quasi-simultaneous radio/optical/X-ray and gamma-ray observations are presented. Both radio and gamma-ray emissions (observed over five months) are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broadband spectral energy distribution (SED) and, in particular, the gamma-ray spectrum measured by Fermi are similar to those of more powerful Flat-Spectrum Radio Quasars (FSRQs). A comparison of the radio and gamma-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and gamma-ray power with respect to other FSRQs. The physical parameters obtained from modeling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti & Ghisellini. We suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.

  • 5. Abdo, A. A.
    et al.
    Ackermann, M.
    Atwood, W. B.
    Axelsson, Magnus
    Johannesson, G.
    Johnson, A. S.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ziegler, M.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    PULSED GAMMA RAYS FROM THE MILLISECOND PULSAR J0030+0451 WITH THE FERMI LARGE AREA TELESCOPE2009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, no 2, p. 1171-1177Article in journal (Refereed)
    Abstract [en]

    We report the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar (MSP) PSR J0030+0451 with the Large Area Telescope on the Fermi Gamma-ray Space Telescope (formerly GLAST). This discovery makes PSR J0030+0451 the second MSP to be detected in gamma rays after PSR J0218+4232, observed by the EGRET instrument on the Compton Gamma-Ray Observatory. The spin-down power (E) over dot = 3.5 x 10(33) erg s(-1) is an order of magnitude lower than the empirical lower bound of previously known gamma-ray pulsars. The emission profile is characterized by two narrow peaks, 0.07 +/- 0.01 and 0.08 +/- 0.02 wide, respectively, separated by 0.44 +/- 0.02 in phase. The first gamma-ray peak falls 0.15 +/- 0.01 after the main radio peak. The pulse shape is similar to that of the "normal" gamma-ray pulsars. An exponentially cutoff power-law fit of the emission spectrum leads to an integral photon flux above 100 MeV of (6.76 +/- 1.05 +/- 1.35) x 10(-8) cm(-2) s(-1) with cutoff energy (1.7 +/- 0.4 +/- 0.5) GeV. Based on its parallax distance of (300 +/- 90) pc, we obtain a gamma-ray efficiency L-gamma/E similar or equal to 15% for the conversion of spin-down energy rate into gamma-ray radiation, assuming isotropic emission.

  • 6. Abdo, A. A.
    et al.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    McGlynn, Sinéad
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ziegler, M.
    et al.,
    EARLY FERMI GAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE QUASAR 3C 454.32009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, no 1, p. 817-823Article in journal (Refereed)
    Abstract [en]

    This is the first report of Fermi Gamma-Ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope, covering 2008 July 7-October 6, indicate strong, highly variable.-ray emission with an average flux of similar to 3 x 10 (6) photons cm(-2) s(-1), for energies > 100 MeV. The gamma-ray flux is variable, with strong, distinct, symmetrically shaped flares for which the flux increases by a factor of several on a timescale of about 3 days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair production implies relativistic beaming with Doppler factor delta > 8, consistent with the values inferred from Very Long Baseline Interferometry observations of superluminal expansion (delta similar to 25). The observed gamma-ray spectrum is not consistent with a simple power law, but instead steepens strongly above similar to 2 GeV, and is well described by a broken power law with photon indices of similar to 2.3 and similar to 3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high-luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to gamma-ray absorption via photon-photon pair production on the soft X-ray photon field of the host active galactic nucleus, but such an interpretation would require the dissipation region to be located very close (less than or similar to 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.

  • 7. Abdo, A. A.
    et al.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    McGlynn, Sinéad
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ziegler, M.
    Moretti, Elena
    University and INFN of Trieste.
    Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C2009In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 323, no 5922, p. 1688-1693Article in journal (Refereed)
    Abstract [en]

    Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.

  • 8. Aharonian, F.
    et al.
    Akhperjanian, A. G.
    Anton, G.
    Barres De Almeida, U.
    Bazer-Bachi, A. R.
    Becherini, Y.
    Behera, B.
    Bernloehr, K.
    Boisson, C.
    Bochow, A.
    Borrel, V.
    Brion, E.
    Brucker, J.
    Brun, P.
    Buehler, R.
    Bulik, T.
    Buesching, I.
    Boutelier, T.
    Chadwick, P. M.
    Charbonnier, A.
    Chaves, R. C. G.
    Cheesebrough, A.
    Chounet, L. -M
    Clapson, A. C.
    Coignet, G.
    Dalton, M.
    Daniel, M. K.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    Dickinson, H. J.
    Djannati-Ata, A.
    Domainko, W.
    O'C. Drury, L.
    Dubois, F.
    Dubus, G.
    Dyks, J.
    Dyrda, M.
    Egberts, K.
    Emmanoulopoulos, D.
    Espigat, P.
    Farnier, C.
    Feinstein, F.
    Fiasson, A.
    Foerster, A.
    Fontaine, G.
    Fuessling, M.
    Gabici, S.
    Gallant, Y. A.
    Gerard, L.
    Giebels, B.
    Glicenstein, J. F.
    Glueck, B.
    Goret, P.
    Goehring, D.
    Hauser, D.
    Hauser, M.
    Heinz, S.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hinton, J. A.
    Hoffmann, A.
    Hofmann, W.
    Holleran, M.
    Hoppe, S.
    Horns, D.
    Jacholkowska, A.
    De Jager, O. C.
    Jahn, C.
    Jung, I.
    Katarzyński, K.
    Katz, U.
    Kaufmann, S.
    Kendziorra, E.
    Kerschhaggl, M.
    Khangulyan, D.
    Khélifi, B.
    Keogh, D.
    Kluzniak, W.
    Komin, N.
    Kosack, K.
    Lamanna, G.
    Lenain, J. -P
    Lohse, T.
    Marandon, V.
    Martin, J. M.
    Martineau-Huynh, O.
    Marcowith, A.
    Maurin, D.
    McComb, T. J. L.
    Medina, M. C.
    Moderski, R.
    Moulin, E.
    Naumann-Godo, M.
    De Naurois, M.
    Nedbal, D.
    Nekrassov, D.
    Niemiec, J.
    Nolan, S. J.
    Ohm, S.
    Olive, J. -F
    De Wilhelmi, E.
    Orford, K. J.
    Ostrowski, M.
    Panter, M.
    Arribas, M. P.
    Pedaletti, G.
    Pelletier, G.
    Petrucci, P. -O
    Pita, S.
    Paehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raubenheimer, B. C.
    Raue, M.
    Rayner, S. M.
    Renaud, M.
    Rieger, F.
    Ripken, J.
    Rob, L.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Ruppel, J.
    Sahakian, V.
    Santangelo, A.
    Schlickeiser, R.
    Schock, F. M.
    Schröder, R.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Shalchi, A.
    Sikora, M.
    Skilton, J. L.
    Sol, H.
    Spangler, D.
    Stawarz, Ł.
    Steenkamp, R.
    Stegmann, C.
    Superina, G.
    Szostek, A.
    Tam, P. H.
    Tavernet, J. -P
    Terrier, R.
    Tibolla, O.
    Van Eldik, C.
    Vasileiadis, G.
    Venter, C.
    Venter, L.
    Vialle, J. P.
    Vincent, P.
    Vivier, M.
    Vaelk, H. J.
    Volpe, F.
    Wagner, S. J.
    Ward, M.
    Zdziarski, A. A.
    Zech, A.
    Abdo, A. A.
    Ackermann, M.
    Ajello, M.
    Atwood, W. B.
    Axelsson, Magnus
    Department of Astronomy, Stockholm University.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics.
    Baughman, B. M.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Casandjian, J. M.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chen, A. W.
    Cheung, C. C.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Colafrancesco, S.
    Conrad, Jan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Costamante, L.
    Cutini, S.
    Dermer, C. D.
    De Angelis, A.
    De Palma, F.
    Digel, S. W.
    Do Couto E Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Fleury, P.
    Focke, W. B.
    Frailis, M.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Grondin, M. -H
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hanabata, Y.
    Harding, A. K.
    Hayashida, M.
    Hays, E.
    Horan, D.
    Jóhannesson, G.
    Johnson, A. S.
    Johnson, R. P.
    Johnson, W. N.
    Kadler, M.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kerr, M.
    Knödlseder, J.
    Kuehn, F.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Lemoine-Goumard, M.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Madejski, G. M.
    Makeev, A.
    Mazziotta, M. N.
    McEnery, J. E.
    Meurer, C.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nolan, P. L.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Rainò, S.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Rodriguez, A. Y.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sadrozinski, H. F. -W
    Sanchez, D.
    Sander, A.
    Scargle, J. D.
    Schalk, T. L.
    Sellerholm, A.
    Sgro, C.
    Shaw, M.
    Smith, D. A.
    Spandre, G.
    Spinelli, P.
    Starck, J. -L
    Strickman, M. S.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Uchiyama, Y.
    Usher, T. L.
    Vilchez, N.
    Villata, M.
    Vitale, V.
    Waite, A. P.
    Wood, K. S.
    Ylinen, Tomi
    KTH, School of Engineering Sciences (SCI), Physics.
    Ziegler, M.
    Simultaneous observations of pks 2155-304 with hess, fermi, rxte, and atom: Spectral energy distributions and variability in a low state2009In: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 696, no 2 PART 2, p. L150-L155Article in journal (Refereed)
    Abstract [en]

    We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of gamma-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; > 100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little (similar to 30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.

  • 9. Band, D. L.
    et al.
    Axelsson, Magnus
    Ist Nazl Fis Nucl, Sez Pisa, Pisa, Italy .
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    McGlynn, Sinéad
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Moretti, Elena
    University and INFN of Trieste.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Yamazaki, R.
    et al.,
    PROSPECTS FOR GRB SCIENCE WITH THE FERMI LARGE AREA TELESCOPE2009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 701, no 2, p. 1673-1694Article, review/survey (Refereed)
    Abstract [en]

    The Large Area Telescope (LAT) instrument on the Fermi mission will reveal the rich spectral and temporal gamma-ray burst (GRB) phenomena in the > 100 MeV band. The synergy with Fermi's Gamma-ray Burst Monitor detectors will link these observations to those in the well explored 10-1000 keV range; the addition of the > 100 MeV band observations will resolve theoretical uncertainties about burst emission in both the prompt and afterglow phases. Trigger algorithms will be applied to the LAT data both onboard the spacecraft and on the ground. The sensitivity of these triggers will differ because of the available computing resources onboard and on the ground. Here we present the LAT's burst detection methodologies and the instrument's GRB capabilities.

  • 10.
    Ryde, Felix
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Axelsson, M.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zhang, B. B.
    McGlynn, S.
    Pe'er, A.
    Lundman, Christoffer
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, S.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zhang, B.
    Bissaldi, E.
    Bregeon, J.
    Briggs, M. S.
    Chiang, J.
    de Palma, F.
    Guiriec, S.
    Larsson, J.
    Longo, F.
    McBreen, S.
    Omodei, N.
    Petrosian, V.
    Preece, R.
    van der Horst, A. J.
    IDENTIFICATION AND PROPERTIES OF THE PHOTOSPHERIC EMISSION IN GRB090902B2010In: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8213, Vol. 709, no 2, p. L172-L177Article in journal (Refereed)
    Abstract [en]

    The Fermi Gamma-ray Space Telescope observed the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover the spectral range from 8 keV to >300 GeV. Here we show that the prompt burst spectrum is consistent with emission from the jet photosphere combined with nonthermal emission described by a single power law with photon index -1.9. The photosphere gives rise to a strong quasi-blackbody spectrum which is somewhat broader than a single Planck function and has a characteristic temperature of similar to 290 keV. We model the photospheric emission with a multicolor blackbody, and its shape indicates that the photospheric radius increases at higher latitudes. We derive the averaged photospheric radius R-ph = (1.1 +/- 0.3) x 10(12) Y-1/4 cm and the bulk Lorentz factor of the flow, which is found to vary by a factor of 2 and has a maximal value of Gamma = 750 Y-1/4. Here, Y is the ratio between the total fireball energy and the energy emitted in the gamma rays. We find that during the first quarter of the prompt phase the photospheric emission dominates, which explains the delayed onset of the observed flux in the LAT compared to the GBM. We interpret the broadband emission as synchrotron emission at R similar to 4 x 10(15) cm. Our analysis emphasizes the importance of having high temporal resolution when performing spectral analysis on gamma-ray bursts, since there is strong spectral evolution.

  • 11.
    Ryde, Felix
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Pe'er, Asaf
    Harvard-Smithsonian Center for Astrophysics, United States.
    Nymark, Tanja
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Moretti, Elena
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Lundman, Christoffer
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Battelino, Milan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Bissaldi, Elisabetta
    Leopold-Franzens-Universität Innsbruck, Austria.
    Chiang, James
    Stanford University, United States.
    Jackson, Miranda S.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, Sweden.
    Larsson, Stefan
    Stockholm University, Sweden.
    Longo, Francesco
    Sezione di Trieste, Italy; Università di Trieste, Italy.
    McGlynn, Sinead
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Technische Universität München, Germany.
    Omodei, Nicola
    Stanford University, United States.
    Observational evidence of dissipative photospheres in gamma-ray bursts2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 415, no 4, p. 3693-3705Article in journal (Refereed)
    Abstract [en]

    The emission from a gamma-ray burst (GRB) photosphere can give rise to a variety of spectral shapes. The spectrum can retain the shape of a Planck function or it can be broadened and have the shape of a Band function. This fact is best illustrated by studying GRB090902B. The main gamma-ray spectral component is initially close to a Planck function, which can only be explained by emission from the jet photosphere. Later, the same component evolves into a broader Band function. This burst thus provides observational evidence that the photosphere can give rise to a non-thermal spectrum. We show that such a broadening is most naturally explained by subphotospheric dissipation in the jet. The broadening mainly depends on the strength and location of the dissipation, the magnetic field strength and the relation between the energy densities of thermal photons and electrons. We suggest that the evolution in spectral shape observed in GRB090902B is due to a decrease in the bulk Lorentz factor of the flow, leading to the main dissipation becoming subphotospheric. Such a change in the flow parameters can also explain the correlation observed between the peak energy of the spectrum and low-energy power-law slope, a, a correlation commonly observed in GRBs. We conclude that photospheric emission could indeed be a ubiquitous feature during the prompt phase in GRBs and play a decisive role in creating the diverse spectral shapes and spectral evolutions that are observed.

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