Статья

GRB 061121: Broadband spectral evolution through the prompt and afterglow phases of a bright burst

K. L. PageDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKR. WillingaleDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKJ. P. OsborneDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKO. GodetDepartment of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154-4002Godet, ODepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKE. RolNASA Goddard Space Flight Center, Greenbelt, MD 20771R. L. C. StarlingAstrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD, UKA. P. BeardmoreVisiting Scholar, Stanford UniversityN. GehrelsDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKPal'shin, VIoffe Physico-Technical Institute, Laboratory for Experimental Astrophysics, Saint Petersburg 194021, Russian FederationE. TrojaDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKBing ZhangDipartimento di Fisica, Universitá di Milano-Bicocca, I-20126 Milano, ItalyF. E. MarshallDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKN. GehrelsUniversity of Michigan, Ann Arbor, MI 48104T. SakamotoNASA Goddard Space Flight Center, Greenbelt, MD 20771M. StamatikosDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKA. MelandriINAF-IASF, Sezione di Palermo, 90146 Palermo, ItalyC. G. MundellDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802J. P. NorrisMullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UKEhle, MXMM-Newton Science Operations Centre, European Space Agency, Villafranca del Castillo, E-28080 Madrid, SpainS. GolenetskiiDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKM. UlanovNASA Goddard Space Flight Center, Greenbelt, MD 20771P. RomanoDepartment of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UKC. GuidorziIoffe Physico-Technical Institute, Laboratory for Experimental Astrophysics, Saint Petersburg 194021, Russian FederationH. ZiaeepourDipartimento di Fisica, Universitá di Milano-Bicocca, I-20126 Milano, ItalyP. SchadyAstrophysics Research Institute, Liverpool John Moores University, Egerton Wharf, Birkenhead CH41 1LD, UKPage, MJMullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UKM. J. PageCenter for Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139S. A. YostNASA Goddard Space Flight Center, Greenbelt, MD 20771F. YuanDepartment of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803G. CusumanoNASA Goddard Space Flight Center, Greenbelt, MD 20771D. N. BurrowsINAF-IASF, Sezione di Palermo, 90146 Palermo, ItalyM. EhleIoffe Physico-Technical Institute, Laboratory for Experimental Astrophysics, Saint Petersburg 194021, Russian FederationG. RickerUniversity of Michigan, Ann Arbor, MI 48104Bradley E. SchaeferDipartimento di Fisica, Universitá di Milano-Bicocca, I-20126 Milano, Italy

2007en

ABI

Аннотация

Swift triggered on a precursor to the main burst of GRB 061121 (z=1.314), allowing observations to be made from the optical to gamma-ray bands. Many other telescopes, including Konus-Wind, XMM-Newton, ROTSE and the Faulkes Telescope North, also observed the burst. The gamma-ray, X-ray and UV/optical emission all showed a peak ~75s after the trigger, although the optical and X-ray afterglow components also appear early on - before, or during, the main peak. Spectral evolution was seen throughout the burst, with the prompt emission showing a clear positive correlation between brightness and hardness. The Spectral Energy Distribution (SED) of the prompt emission, stretching from 1eV up to 1MeV, is very flat, with a peak in the flux density at ~1keV. The optical-to-X-ray spectra at this time are better fitted by a broken, rather than single, power-law, similar to previous results for X-ray flares. The SED shows spectral hardening as the afterglow evolves with time. This behaviour might be a symptom of self-Comptonisation, although circumstellar densities similar to those found in the cores of molecular clouds would be required. The afterglow also decays too slowly to be accounted for by the standard models. Although the precursor and main emission show different spectral lags, both are consistent with the lag-luminosity correlation for long bursts. GRB 061121 is the instantaneously brightest long burst yet detected by Swift. Using a combination of Swift and Konus-Wind data, we estimate an isotropic energy of 2.8x10^53 erg over 1keV - 10MeV in the GRB rest frame. A probable jet break is detected at ~2x10^5s, leading to an estimate of ~10^51 erg for the beaming-corrected gamma-ray energy.

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