Статья

Evidence for a Canonical Gamma‐Ray Burst Afterglow Light Curve in the<i>Swift</i>XRT Data

J. A. NousekDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802C. KouveliotouNASA Marshall Space Flight Center, National Space Science Technology Center, XD-12, 320 Sparkman Drive, Huntsville, AL 35805D. GrupeDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802K. L. PageDepartment of Physics and Astronomy, University of Leicester, Leicester, UKJonathan GranotKavli Institute for Particle Astrophysics and Cosmology, Stanford University, P.O. Box 20450, MS 29, Stanford, CA 94309E. Ramírez-RuizChandra FellowS. PatelIPA with NASA/MSFC through Universities Space Research AssociationD. N. BurrowsDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802V. ManganoINAF - Istituto di Fisica Spazialee Fisica Cosmica Sezione di Palermo, Palermo, ItalyA. P. BeardmoreNASA Goddard Space Flight Center, Greenbelt, MD 20771S. CampanaINAF - Osservatorio Astronomico di Brera, Merate, ItalyM. CapalbiG. ChincariniINAF - Osservatorio Astronomico di Brera, Merate, ItalyG. CusumanoINAF - Istituto di Fisica Spazialee Fisica Cosmica Sezione di Palermo, Palermo, ItalyA. FalconeDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802N. GehrelsNASA Goddard Space Flight Center, Greenbelt, MD 20771P. GiommiM. R. GoadDepartment of Physics and Astronomy, University of Leicester, Leicester, UKO. GodetDepartment of Physics and Astronomy, University of Leicester, Leicester, UKC. P. HurkettDepartment of Physics and Astronomy, University of Leicester, Leicester, UKJ. A. KenneaDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802A. MorettiINAF - Osservatorio Astronomico di Brera, Merate, ItalyP. T. O’BrienDepartment of Physics and Astronomy, University of Leicester, Leicester, UKJ. P. OsborneDepartment of Physics and Astronomy, University of Leicester, Leicester, UKP. RomanoINAF - Osservatorio Astronomico di Brera, Merate, ItalyG. TagliaferriINAF - Osservatorio Astronomico di Brera, Merate, ItalyA. A. WellsDepartment of Physics and Astronomy, University of Leicester, Leicester, UK

2006en

ABI

Аннотация

We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) detected with the Swift X-ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power law segments: (i) an initial very steep decay (t^{-alpha} with 3<alpha_1<5), followed by (ii) a very shallow decay (0.2<alpha_2<0.8), and finally (iii) a somewhat steeper decay (1<alpha_3<1.5). These power law segments are separated by two corresponding break times, 300s<t_{break,1}<500s and 10^3s<t_{break,2}<10^4s. On top of this canonical behavior of the early X-ray light curve, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (t_{break,1}) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (alpha_2) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (t_{break,2}). This energy injection increases the energy of the afterglow shock by at least a factor of f>4, and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

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Идентификаторы

DOI: 10.1086/500724

Цитирования и источники

Цитирований: 9Использованных источников: 0

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