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arXiv 1202.3443astro-ph.HE
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观测者和源静止坐标系中斯威夫特长伽马射线暴的平均功率密度谱

Average power density spectrum of Swift long gamma-ray bursts in the observer and in the source rest frames

C. Guidorzi, R. Margutti, L. Amati, S. Campana, M. Orlandini, P. Romano, M. Stamatikos, G. Tagliaferri

摘要:

计算了2005年1月至2011年8月雨燕暴警报望远镜在15-150 keV波段探测到的244个长伽马射线暴的平均功率密度谱。首次导出了97个已知红移的伽玛暴在源静止坐标系中的平均PDS。对于其中的49个平均PDS也得到了在一个共同的源帧的能量带占的时间分布对能量的依赖性。先前在具有未知红移的BATSE伽玛暴上获得的结果表明,在25-2000 keV波段的平均谱可以用幂律建模,在近20年的频率上具有5/3指数,在~1 Hz处有一个中断。根据归一化和考虑的伽玛暴的子集,我们的结果显示类似于陡峭的斜率(1.7和2.0之间)的幂律。然而,没有发现在~1 Hz处断裂的明确证据,尽管BAT与BATSE相比的较软能带可能解释了这一点。相反,我们发现在较低的频率对应于一个典型的源休息帧的特征时间为几秒钟的休息。此外,我们发现观察者和源休息帧之间没有显着差异。值得注意的是,没有发现显着的PDS功能与不同的本征性质的即时发射的伽玛暴。最后,在高红移的伽玛暴的平均PDS显示可能比低z伽玛暴更浅的幂律指数。尚不清楚这是否是由于平均PDS随z的演变。

英文摘要:

We calculate the average power density spectra (PDS) of 244 long gamma-ray bursts detected with the Swift Burst Alert Telescope in the 15-150 keV band from January 2005 to August 2011. For the first time we derived the average PDS in the source rest frame of 97 GRBs with known redshift. For 49 of them an average PDS was also obtained in a common source-frame energy band to account for the dependence of time profiles on energy. Previous results obtained on BATSE GRBs with unknown redshift showed that the average spectrum in the 25-2000 keV band could be modelled with a power-law with a 5/3 index over nearly two decades of frequency with a break at ~1 Hz. Depending on the normalisation and on the subset of GRBs considered, our results show analogous to steeper slopes (between 1.7 and 2.0) of the power-law. However, no clear evidence for the break at ~1 Hz was found, although the softer energy band of BAT compared with BATSE might account for that. We instead find a break at lower frequency corresponding to a typical source rest frame characteristic time of a few seconds. We furthermore find no significant differences between observer and source rest frames. Notably, no distinctive PDS features are found for GRBs with different intrinsic properties of the prompt emission either. Finally, the average PDS of GRBs at higher redshifts shows possibly shallower power-law indices than that of low-z GRBs. It is not clear whether this is due to an evolution with z of the average PDS.

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