Burrows 200 7 SwiftX射线余辉无喷流拐折

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astro-ph/0702633 [abs, ps, pdf, other] :

Title: Swift X-ray Afterglows: Where are the X-ray Jet Breaks?
Authors: David N. Burrows, Judith Racusin
Comments: 13 pages; 15 figures; Proceeding of the "Swift and GRBs: Unveiling the Relativistic Universe" meeting,Venice, June 5-9,2006, to be published by "Il Nuovo Cimento"

We examine the Swift/X-ray Telescope (XRT) light curves from the first ~150 gamma-ray burst (GRB) afterglows. Although we expected to find jet breaks at typical times of 1-2 days after the GRB, we find that these appear to be extremely rare. Typical light curves have a break in the slope at about 10^4s, followed by a single power-law decay whose slope is much too shallow to be consistent with expectations for jet breaks. X-ray light curves typically extend out to ~10 days without any further breaks, until they become too faint for the XRT to detect. In some extreme cases, light curves extend out to more than two months without evidence for jet breaks. This raises concerns about our understanding of afterglow and jet dynamics, and of GRB energetics.