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Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data

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posted on 2016-05-12, 11:39 authored by J. A. Nousek, C. Kouveliotou, D. Grupe, K. L. Page, J. Granot, E. Ramirez-Ruiz, S. K. Patel, D. N. Burrows, V. Mangano, S. Barthelmy, A. P. Beardmore, S. Campana, M. Capalbi, G. Chincarini, G. Cusumano, A. D. Falcone, N. Gehrels, P. Giommi, M. R. Goad, O. Godet, Cheryl Hurkett, J. A. Kennea, A. Moretti, P. T. O'Brien, J. P. Osborne, P. Romano, G. Tagliaferri, A. A. Wells
We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by 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: (1) an initial very steep decay (∝t-α with 3 lesssim α1 lesssim 5), followed by (2) a very shallow decay (0.5 lesssim α2 lesssim 1.0), and finally (3) a somewhat steeper decay (1 lesssim α3 lesssim 1.5). These power-law segments are separated by two corresponding break times, tbreak,1 lesssim 500 s and 103 s lesssim tbreak,2 lesssim 104 s. On top of this canonical behavior, 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 (tbreak,1) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (α2) 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 (tbreak,2). This energy injection increases the energy of the afterglow shock by at least a factor of f gsim 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

History

Citation

The Astrophysical Journal, 2006, 642 (1), pp. 389-400

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

The Astrophysical Journal

Publisher

American Astronomical Society

issn

0004-637X

eissn

1538-4357

Acceptance date

2005-12-22

Copyright date

2006

Available date

2016-05-12

Publisher version

http://iopscience.iop.org/article/10.1086/500724/meta

Language

en