Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/18794
 Title: Long-term monitoring of the X-ray afterglow of GRB 050408 with Swift/XRT Authors: Capalbi, M.Perri, M.Giommi, P.Malesani, D.Giommi, P.Covino, S.Campana, S.Chincarini, G.Moretti, A.Romano, P.Tagliaferri, G.Cusumano, G.Mangano, V.Mineo, T.La Parola VChincarini, G.Angelini, L.Boyd, P.Hill, J. E.Marshall, F.Gehrels, N.Angelini, L.Burrows, D. N.Kennea, J. A.Godet, O.O'Brien, P. T.Hill, J. E. First Published: Feb-2007 Publisher: EDP Sciences for European Southern Observatory (ESO) Citation: Astronomy & Astrophysics, 2007, 462 (3), pp. 913-918 Abstract: We present observations of the X-ray afterglow of GRB 050408, a gamma-ray burst discovered by HETE-II. Swift began observing the field 42 min after the burst, performing follow-up over a period of 38 d (thus spanning three decades in time). The X-ray light curve showed a steepening with time, similar to many other afterglows. However, the steepening was unusually smooth, over the duration of the XRT observation, with no clear break time. The early decay was too flat to be described in terms of standard models. We therefore explore alternative explanations, such as the presence of a structured afterglow or of long-lasting energy injection into the fireball from the central GRB engine. The lack of a sharp break puts constraints on these two models. In the former case, it may indicate that the angular energy profile of the jet was not a simple power law, while in the second model it implies that injection did not stop abruptly. The late decay may be due either to a standard afterglow (that is with no energy injection), or to a jetted outflow still being refreshed. A significant amount of absorption was present in the X-ray spectrum, corresponding to a rest-frame hydrogen column density $N_{\rm H} = 1.2_{-0.3}^{+0.4} \times 10^{22}$ cm-2, indicative of a dense environment. DOI Link: 10.1051/0004-6361:20065388 ISSN: 0004-6361 eISSN: 1432-0746 Links: http://hdl.handle.net/2381/18794http://www.aanda.org/articles/aa/abs/2007/06/aa5388-06/aa5388-06.html Version: Publisher Version Status: Peer-reviewed Type: Journal Article Rights: Copyright © 2007 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO. Appears in Collections: Published Articles, Dept. of Physics and Astronomy

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