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Title: Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data
Authors: Nousek, J. A.
Kouveliotou, C.
Grupe, D.
Page, K. L.
Granot, J.
Ramirez-Ruiz, E.
Patel, S. K.
Burrows, D. N.
Mangano, V.
Barthelmy, S.
Beardmore, A. P.
Campana, S.
Capalbi, M.
Chincarini, G.
Cusumano, G.
Falcone, A. D.
Gehrels, N.
Giommi, P.
Goad, M. R.
Godet, O.
Hurkett, Cheryl
Kennea, J. A.
Moretti, A.
O'Brien, P. T.
Osborne, J. P.
Romano, P.
Tagliaferri, G.
Wells, A. A.
First Published: 1-May-2006
Publisher: American Astronomical Society
Citation: The Astrophysical Journal, 2006, 642 (1), pp. 389-400
Abstract: 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.
DOI Link: 10.1086/500724
ISSN: 0004-637X
eISSN: 1538-4357
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright (c) 2006 The American Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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