Liang 2007 Swift暴X射线的平降阶段统计分析

主要内容:
分析了从050318到070129的swift的暴的X射线余辉光变。给出了各单个暴的特征量和特征量的统计。

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文章信息:
arXiv:0705.1373 [ps, pdf, other] : Title: A Comprehensive Analysis of the Swift/XRT Data: II. Diverse Physical Origins of the Shallow Decay Segment
Authors: En-Wei Liang, Bin-Bin Zhang, Bing Zhang
Comments: 25 pages in emulateapj style, 7 figures, submitted to ApJ. This is the second paper of a series. Paper I see astro-ph/0612246

A shallow decay segment following the GRB tail is usually seen in the Swift XRT light curves, which transits to a steeper decay segment at the break time t_b. Its physical origin is a great puzzle. We present a comprehensive analysis to this segment for a sample of 48 long GRBs discovered by Swift before February 2007 that display such a distinct phase. We show that (1)no significant spectral evolution is observed across t_b, and the follow-up decay phase is consistent with the simplest external shock models for most bursts; (2)for these bursts, an empirical relation among E_iso, X, E_p, and t_b is found in the burst rest frame; (3) at least the t_b of some bursts are chromatic; (4) three outliers of the external shock models, GRBs 060413, 060607A, and 070110, have an abrupt drop at t_b, and the t_b is chromatic for the latter two bursts with simultaneous optical detections. These results suggest diverse, complicated physical origins for the shallow decay segment and its t_b. Most bursts in our sample are consistent with being due to long-lived energy injection (generally with a roughly constant injection luminosity up to t_b, although the fact that at least some breaks are chromatic raises great concern to such a scenario. The three significant outliers cannot be explained within the external shock models. These plateaus are probably due to a steady, long-lived emission component from the GRB central engine. Therefore, the XRT light curves are possibly composed of different emission components, and the competition of them makes the variety of the light curves observed by XRT (Abridged).