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Title: The early X-ray emission from GRBs
Authors: O'Brien, Paul T.
Willingale, Richard
Osborne, Julian P.
Goad, Michael R.
Page, Kim L.
Vaughan, Simon A.
Rol, Evert
Beardmore, Andrew P.
Godet, Olivier
Hurkett, C. P.
Wells, Alan A.
Zhang, B.
Kobayashi, Shiho
Burrows, David N.
Nousek, John A.
Kennea, Jamie A.
Falcone, Abraham D.
Grupe, Dirk
Gehrels, Neil
Barthelmy, Scott D.
Cannizzo, J.
Cummings, J. R.
Hill, Joanne E.
Krimm, H.
Chincarini, Guido
Tagliaferri, Gianpiero
Campana, Sergio
Moretti, Alberto
Giommi, Paolo
Perri, M.
Mangano, V.
La Parola, V.
First Published: 20-Aug-2006
Publisher: IOP Science
Citation: Astrophysical Journal, 2006, 647(2), pp.1213-1237.
Abstract: We present observations of the early X-ray emission for a sample of 40 gamma-ray bursts (GRBs) obtained using the Swift satellite, for which the narrow-field instruments were pointed at the burst within 10 minutes of the trigger. Using data from the Burst Alert Telescope and the X-Ray Telescope, we show that the X-ray light curve can be well described by an exponential that relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law provides a physically defined timescale for the burst duration. In most bursts, the power law breaks to a shallower decay within the first hour, and a late emission "hump" is observed, which can last for many hours. In other GRBs the hump is weak or absent. The observed variety in the shape of the early X-ray light curve can be explained as a combination of three components: prompt emission from the central engine, afterglow, and the late hump. In this scenario, afterglow emission begins during or soon after the burst, and the observed shape of the X-ray light curve depends on the relative strengths of the emission due to the central engine and that of the afterglow. There is a strong correlation such that those GRBs with stronger afterglow components have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. GRBs with the strongest late humps have weak or no X-ray flares.
DOI Link: 10.1086/505457
ISSN: 0004-637X
eISSN: 1538-4357
Version: Post-print
Status: Peer-reviewed
Type: Article
Rights: © 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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