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2015 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 813, no 2, 127Article in journal (Refereed) PublishedText
Abstract [en]

We study the properties of a significant thermal emission component that was identified in 47 gamma-ray bursts observed by different instruments. Within the framework of the "fireball" model, we deduce the values of the Lorentz factor Gamma, and the acceleration radius, r(0), for these bursts. We find that all the values of Gamma in our sample are in the range 10(2) <= Gamma <= 10(3), with <Gamma > = 370. We find a very weak dependence of Gamma on the acceleration radius r0, Gamma proportional to r(0)(alpha) with alpha - -0.10 +/- 0.09 at the sigma - 2.1 confidence level. The values of r(0) span a wide range, 10(6.5) <= r(0) <= 10(9.5) cm, with a mean value of < r(0)> similar to 10(8) cm. This is higher than the gravitational radius of a 10 M-circle dot black hole by a factor of approximate to 30. We argue that this result provides indirect evidence for jet propagation inside a massive star, and suggests the existence of recollimation shocks that take place close to this radius.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2015. Vol. 813, no 2, 127
Keyword [en]
gamma rays, stars, hydrodynamics, methods: data analysis, radiation mechanisms, thermal, radiative transfer
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-179598DOI: 10.1088/0004-637X/813/2/127ISI: 000365288900047ScopusID: 2-s2.0-84947967922OAI: diva2:893106


Available from: 2016-01-12 Created: 2015-12-17 Last updated: 2016-01-12Bibliographically approved

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Ryde, FelixLarsson, Josefin
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