<i>FERMI</i> OBSERVATIONS OF GRB 090902B: A DISTINCT SPECTRAL COMPONENT IN THE PROMPT AND DELAYED EMISSION
A. A. AbdoNational Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USAM. AckermannW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAM. AjelloW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAKatsuaki AsanoDepartment of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, JapanW. B. AtwoodSanta Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USAM. AxelssonDepartment of Astronomy, Stockholm University, SE-106 91 Stockholm, SwedenL. BaldiniIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyJ. BalletLaboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, FranceG. BarbielliniDipartimento di Fisica, Università di Trieste, I-34127 Trieste, ItalyMatthew G. BaringRice University, Department of Physics and Astronomy, MS-108, P.O. Box 1892, Houston, TX 77251, USAD. BastieriDipartimento di Fisica “G. Galilei,” Università di Padova, I-35131 Padova, ItalyK. BechtolW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAR. BellazziniIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyB. BerenjiW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. N. BhatUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAC. MeeganMax-Planck Institut für extraterrestrische Physik, 85748 Garching, GermanyR. D. BlandfordW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAE. D. BloomW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAE. BonamenteDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyA. W. BorglandW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAA. BouvierW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAJ. BregeonIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyA. BrezIstituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, ItalyM. S. BriggsUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAM. BrigidaDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyP. BruelLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, FranceJ. Michael BurgessUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAD. BurrowsDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USAS. BusonDipartimento di Fisica “G. Galilei,” Università di Padova, I-35131 Padova, ItalyG. A. CaliandroDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyR. A. CameronW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. A. CaraveoINAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, ItalyJ. M. CasandjianLaboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, FranceC. CecchiDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyÖ. ÇelikCenter for Research and Exploration in Space Science and Technology (CRESST), NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAA. ChekhtmanGeorge Mason University, Fairfax, VA 22030, USAC. C. CheungNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAJ. ChiangW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAS. CipriniDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyR. ClausW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAJ. Cohen-TanugiLaboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, FranceL. R. CominskyDepartment of Physics and Astronomy, Sonoma State University, Rohnert Park, CA 94928-3609, USAV. ConnaughtonUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAJ. M. ConradDepartment of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, SwedenS. CutiniAgenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), ItalyV. D’EliaAgenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), ItalyC. D. DermerSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAA. De AngelisDipartimento di Fisica, Università di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, ItalyF. de PalmaDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyS. W. DigelStanford UniversityB. L. DingusLos Alamos National Laboratory, Los Alamos, NM 87545, USAE. do Couto e SilvaW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. S. DrellW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAR. DuboisW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAD. DumoraCNRS/IN2P3, Centre d’Études Nucléaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, FranceC. FarnierLaboratoire de Physique Théorique et Astroparticules, Université Montpellier 2, CNRS/IN2P3, Montpellier, FranceC. FavuzziDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyS. FeganLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, FranceJ. FinkeNational Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USAG. J. FishmanNASA Marshall Space Flight Center, Huntsville, AL 35812, USAW. B. FockeW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. FortinLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, FranceM. FrailisDipartimento di Fisica, Università di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, ItalyY. FukazawaDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, JapanS. FunkW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAP. FuscoDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyF. GarganoIstituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, ItalyN. GehrelsDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USAS. GermaniDipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, ItalyG. GiavittoIstituto Nazionale di Fisica Nucleare, Sezione di Trieste, and Università di Trieste, I-34127 Trieste, ItalyB. GiebelsLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, FranceN. GigliettoDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyF. GiordanoDipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, ItalyT. GlanzmanW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAG. GodfreyKavli Institute for Particle Astrophysics and CosmologyAllen H. GoldsteinUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAJonathan GranotCentre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UKJ. GreinerMax-Planck Institut für extraterrestrische Physik, 85748 Garching, GermanyI. A. GrenierLaboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, FranceJ. E. GroveSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAL. GuillemotMax-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, GermanyS. GuiriecUniversity of Alabama in Huntsville, Huntsville, AL 35899, USAY. HanabataDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, JapanA. K. HardingNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAM. HayashidaW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAE. HaysNASA Goddard Space Flight Center, Greenbelt, MD 20771, USAD. HoranLaboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, FranceR. E. HughesDepartment of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USAM. JacksonDepartment of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, SwedenG. JóhannessonW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAA. S. JohnsonW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAR. P. JohnsonSanta Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064, USAW. N. JohnsonSpace Science Division, Naval Research Laboratory, Washington, DC 20375, USAT. KamaeW. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USAH. KatagiriDepartment of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, JapanJ. KataokaDepartment of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, JapanN. KawaiCosmic Radiation Laboratory, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, JapanM. KerrDepartment of Physics, University of Washington, Seattle, WA 98195-1560, USAR. M. KippenLos Alamos National Laboratory, Los Alamos, NM 87545, USAJ. KnödlsederCentre d’Étude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-30128 Toulouse Cedex 4, France
2009en
ABI
Аннотация
We report on the observation of the bright, long gamma-ray burst, GRB 090902B, by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board the Fermi observatory. This was one of the brightest GRBs to have been observed by the LAT, which detected several hundred photons during the prompt phase. With a redshift of z = 1.822, this burst is among the most luminous detected by Fermi. Time-resolved spectral analysis reveals a significant power-law component in the LAT data that is distinct from the usual Band model emission that is seen in the sub-MeV energy range. This power-law component appears to extrapolate from the GeV range to the lowest energies and is more intense than the Band component both below $\\sim$ 50 keV and above 100 MeV. The Band component undergoes substantial spectral evolution over the entire course of the burst, while the photon index of the power-law component remains constant for most of the prompt phase, then hardens significantly towards the end. After the prompt phase, power-law emission persists in the LAT data as late as 1 ks post-trigger, with its flux declining as $t^{-1.5}$. The LAT detected a photon with the highest energy so far measured from a GRB, $33.4_{-3.5}^{+2.7}$ GeV. This event arrived 82 seconds after the GBM trigger and $\\sim$ 50 seconds after the prompt phase emission had ended in the GBM band. We discuss the implications of these results for models of GRB emission and for constraints on models of the Extragalactic Background Light.
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