Grupe 2009 GRB 060729的晚期X射线余辉

主要内容:
主要是Chandra的观测

精彩摘抄:
光变
多个光变的比较

文章信息:

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Title:		Late-time detections of the X-ray afterglow of GRB 060729 with Chandra - the latest detections ever of an X-ray afterglow
Authors:		Grupe, Dirk; Burrows, David N.; Xue-Feng; Wang, Xiang-Yu; Zhang, Bing; Garmire, Gordon; Nousek, John A.; Gehrels, Neil; Ricker, George; Bautz, Marshall W.
Publication:		eprint arXiv:0903.1258
Publication Date:		03/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		submitted to ApJ, 12 pages, 5 figures, 2 tables
Bibliographic Code:		2009arXiv0903.1258G

Abstract

We report on 5 Chandra observations of the X-ray afterglow of the Gamma-Ray Burst GRB 060729 performed between 2007 March and 2008 May. In all five observations the afterglow is clearly detected. The last Chandra pointing was performed on 2008-May-04, 642 days after the burst - the latest detection of a GRB X-ray afterglow ever. The last two Chandra observations in 2007 December and 2008 May clearly indicate a break at about one year after the burst. If interpreted as a jet break, this late-time break implies a jet half opening angle of ~14 degrees for a wind medium. On the other hand, the steep temporal decay and significant spectral softening after this break favor a spectral origin for the break. In the latter interpretation, no jet break was observed 642 days after the burst indicates the half-opening angle of the jet of GRB 060729 should be larger than >15 degrees for a wind medium. We compare the X-ray afterglow in a wind environment of GRB 060729 with other bright X-ray afterglows, in particular GRBs 061121 and 080319B, and discuss why the X-ray afterglow of GRB 060729 is such an exceptionally long-lasting event. A reanalysis of the Swift XRT light curve together with the three detections by Chandra in 2007 reveal a break at $\sim$1.2 Ms after the burst with a slight steepening of the decay slope from $\alpha$=1.32 to 1.65. This break coincides with a significant hardening of the X-ray spectrum, consistent with a cooling break in the wind medium scenario, in which the cooling frequency of the afterglow just crosses the X-ray band.

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