Journal Article

Testing a new view of gamma-ray burst afterglows

M. Nardini, G. Ghisellini, G. Ghirlanda and A. Celotti

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 3, pages 1131-1142
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2009.16160.x
Testing a new view of gamma-ray burst afterglows

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The optical and X-ray light curves of long gamma-ray bursts (GRBs) often show a complex evolution and in most cases do not track each other. This behaviour cannot be easily explained by the simplest standard afterglow models. A possible interpretation is to consider the observed optical and X-ray light curves as the sum of two separate components. This scenario requires the presence of a spectral break between these bands. One of the aims of this work is to test whether such a break is present within the observed Swift X-Ray Telescope energy range. We analyse the X-ray afterglow spectra of a sample of 33 long GRBs with known redshift, good optical photometry and published estimate of the host galaxy dust absorption AhostV. We find that indeed in seven bright events a broken power law provides a fit to the data that is better than a single power-law model. For eight events, instead, the X-ray spectrum is better fitted by a single power law. We discuss the role of these breaks in connection to the relation between the host hydrogen column density NhostH and AhostV and check the consistency of the X-ray spectral breaks with the optical bands photometry. We analyse the optical to X-ray spectral energy distributions at different times and find again consistency with two components interpretation.

Keywords: gamma-rays: bursts

Journal Article.  9387 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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