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The nature of the outflow in gamma-ray bursts

Kumar, P; McMahon, E; Panaitescu, A; Willingale, R; O'Brien, P; Burrows, D; Cummings, J; ... Zane, S; + view all (2007) The nature of the outflow in gamma-ray bursts. Monthly Notices of the Royal Astronomical Society: Letters , 376 (1) L57 - L61. 10.1111/j.1365-2966.2007.00286.x. Green open access

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The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt gamma-ray emission, the emission that heralds these bursts, is short lived, and is distinct from the source for the long-lived afterglow emission that follows the initial burst. Using these data we determine the distance of the gamma-ray source from the centre of the explosion. We find this distance to be 10(15)-10(16) cm for most bursts, and show that this is within a factor of about 10 of the radius of the shock heated circumstellar medium (CSM) producing the X-ray photons. Furthermore, using the early gamma-ray, X-ray and optical data we show that the prompt gamma-ray emission cannot be produced in internal shocks nor can it be produced in the external shock; in a more general sense gamma-ray generation mechanisms based on shock physics have problems explaining the GRB data for ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has a number of attractive features, although evidence in its favour is inconclusive. Finally, the X-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons cm(-3) at a distance of similar to 5 x 10(16) cm from the centre of explosion.

Type: Article
Title: The nature of the outflow in gamma-ray bursts
Open access status: An open access version is available from UCL Discovery
DOI: 10.1111/j.1365-2966.2007.00286.x
Publisher version: http://dx.doi.org/10.1111/j.1365-2966.2007.00286.x
Language: English
Additional information: © 2007 RAS Definitive versions of articles pre-2013 are available at http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2966, now published by http://mnras.oxfordjournals.org
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/174439
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