Fermi Observations of GRB 090510: A Short Hard Gamma-Ray Burst with an Additional, Hard Power-Law Component from 10 keV to GeV Energies

M. Ackermann K. Asano W. B. Atwood M. Axelsson L. Baldini J. Ballet 1 G. Barbiellini M. G. Baring D. Bastieri K. Bechtol R. Bellazzini 1 B. Berenji P. N. Bhat E. Bissaldi R. D. Blandford E. D. Bloom E. Bonamente A. W. Borgland A. Bouvier J. Bregeon A. Brez M. S. Briggs M. Brigida P. Bruel 2 S. Buson G. A. Caliandro R. A. Cameron P. A. Caraveo S. Carrigan J. M. Casandjian 1 C. Cecchi O. Celik E. Charles 1 J. Chiang S. Ciprini R. Claus J. Cohen-Tanugi 3 V. Connaughton J. Conrad C. D. Dermer F. De Palma B. L. Dingus E. Do Couto E Silva P. S. Drell R. Dubois D. Dumora 4 C. Farnier 3 C. Favuzzi S. J. Fegan 2 J. Finke W. B. Focke M. Frailis Y. Fukazawa P. Fusco F. Gargano D. Gasparrini N. Gehrels S. Germani N. Giglietto F. Giordano T. Glanzman G. Godfrey J. Granot I. A. Grenier 1 M.-H. Grondin 4 J. E. Grove S. Guiriec 3 D. Hadasch A. K. Harding E. Hays D. Horan 2 R. E. Hughes G. Johannesson W. N. Johnson T. Kamae H. Katagiri J. Kataoka N. Kawai R. M. Kippen J. Knodlseder 5 D. Kocevski C. Kouveliotou M. Kuss J. Lande L. Latronico M. Lemoine-Goumard 4 M. Llena Garde F. Longo F. Loparco B. Lott 4 M. N. Lovellette P. Lubrano A. Makeev M. N. Mazziotta J. E. Mcenery S. Mcglynn C. Meegan P. Meszaros P. F. Michelson W. Mitthumsiri T. Mizuno A. A. Moiseev C. Monte M. E. Monzani E. Moretti A. Morselli I. V. Moskalenko S. Murgia H. Nakajima T. Nakamori P. L. Nolan J. P. Norris E. Nuss 3 M. Ohno T. Ohsugi N. Omodei E. Orlando J. F. Ormes M. Ozaki W. S. Paciesas D. Paneque J. H. Panetta D. Parent 4 V. Pelassa 3 M. Pepe M. Pesce-Rollins F. Piron 3 R. Preece S. Raino R. Rando M. Razzano S. Razzaque A. Reimer S. Ritz A. Y. Rodriguez M. Roth F. Ryde H. F.-W. Sadrozinski A. Sander J. D. Scargle 1 T. L. Schalk C. Sgro 2 E. J. Siskind P. D. Smith G. Spandre P. Spinelli M. Stamatikos F. W. Stecker M. S. Strickman D. J. Suson H. Tajima H. Takahashi T. Takahashi T. Tanaka J. B. Thayer J. G. Thayer D. J. Thompson L. Tibaldo 1 K. Toma D. F. Torres G. Tosti A. Tramacere Y. Uchiyama T. Uehara T. L. Usher A. J. Van Der Horst V. Vasileiou N. Vilchez 5 V. Vitale A. Von Kienlin A. P. Waite P. Wang C. Wilson-Hodge B. L. Winer X. F. Wu R. Yamazaki Z. Yang T. Ylinen M. Ziegler
Abstract : We present detailed observations of the bright short-hard gamma-ray burst GRB 090510 made with the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi observatory. GRB 090510 is the first burst detected by the LAT that shows strong evidence for a deviation from a Band spectral fitting function during the prompt emission phase. The time-integrated spectrum is fit by the sum of a Band function with $\Epeak = 3.9\pm 0.3$\,MeV, which is the highest yet measured, and a hard power-law component with photon index $-1.62\pm 0.03$ that dominates the emission below $\approx$\,20\,keV and above $\approx$\,100\,MeV. The onset of the high-energy spectral component appears to be delayed by $\sim$\,0.1\,s with respect to the onset of a component well fit with a single Band function. A faint GBM pulse and a LAT photon are detected 0.5\,s before the main pulse. During the prompt phase, the LAT detected a photon with energy $30.5^{+5.8}_{-2.6}$ GeV, the highest ever measured from a short GRB. Observation of this photon sets a minimum bulk outflow Lorentz factor, $\Gamma\ga$\,1200, using simple $\gamma\gamma$ opacity arguments for this GRB at redshift $z = 0.903$ and a variability time scale on the order of tens of ms for the $\approx$\,100\,keV--few MeV flux. Stricter high confidence estimates imply $\Gamma \ga 1000$ and still require that the outflows powering short GRBs are at least as highly relativistic as those of long duration GRBs. Implications of the temporal behavior and power-law shape of the additional component on synchrotron/synchrotron self-Compton (SSC), external-shock synchrotron, and hadronic models are considered.
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Journal articles
Astrophysical Journal, American Astronomical Society, 2010, 716, pp.1178-1190. <10.1088/0004-637X/716/2/1178>


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Submitted on : Friday, July 2, 2010 - 3:00:40 PM
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M. Ackermann, K. Asano, W. B. Atwood, M. Axelsson, L. Baldini, et al.. Fermi Observations of GRB 090510: A Short Hard Gamma-Ray Burst with an Additional, Hard Power-Law Component from 10 keV to GeV Energies. Astrophysical Journal, American Astronomical Society, 2010, 716, pp.1178-1190. <10.1088/0004-637X/716/2/1178>. <in2p3-00497160>

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