The early X-ray emission from GRBs
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 and X-Ray Telescopes, 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.
Cite
@article{arxiv.astro-ph/0601125,
title = {The early X-ray emission from GRBs},
author = {P. T. O'Brien and R. Willingale and J. Osborne and M. R. Goad and K. L. Page and S. Vaughan and E. Rol and A. Beardmore and O. Godet and C. Hurkett and A. Wells and B. Zhang and S. Kobayashi and D. N. Burrows and J. A. Nousek and J. A. Kennea and A. Falcone and D. Grupe and N. Gehrels and S. Barthelmy and J. Cannizzo and J. Cummings and J. Hill and H. Krimm and G. Chincarini and G. Tagliaferri and S. Campana and A. Moretti and P. Giommi and M. Perri and V. Mangano and V. LaParola},
journal= {arXiv preprint arXiv:astro-ph/0601125},
year = {2010}
}
Comments
Submitted to ApJ on December 16. Revised following referee's comments. Accepted for publication in ApJ. Minor correction to Fig. 14 caption and updated references