Shao 2010 150个有红移的Swift暴的统计

主要内容:
统计包括光变，光子谱指数和红移分布。红移按泊松分布，光子谱在prompt阶段和余辉阶段有个变化，光变在prompt阶段有个平台（意味着中心引擎此时输出的功率一定）。

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Title:		Underlying global features of the X-ray light curves of Swift GRBs
Authors:		Shao, Lang; Fan, Yi-Zhong; Wei, Da-Ming
Publication:		eprint arXiv:1006.0286
Publication Date:		06/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		17 pages, 4 figures
Bibliographic Code:		2010arXiv1006.0286S

Abstract

With its rapid-response, {\it Swift} has revealed plenty of unexpected properties of gamma-ray bursts (GRBs). Primarily, our current understandings are challenged by the observed complex early X-ray light curves. In this {\it Letter}, based on the public {\it Swift} data of 150 well monitored GRBs with measured redshifts, we find some interesting global features of the X-ray light curves in the rest frame. The distinct spectral behaviors between the prompt emission and the afterglow emission implies dissimilar radiation scenarios. Interestingly, an unforeseen plateau is exhibited in the prompt X-ray light curves despite of being full of spikes, which might reveal a steady central engine. In addition, the redshift distribution for the 150 bursts also reveals a Possion quality.

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Rowlinson 2010 GRB 080905A的光学余辉和宿主星系的观测

主要内容:
 z=0.1218, 是目前红移最低的短暴。没有超新星成分。短暴周围没有发射线，说明很有可能是双致密星起源。

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Title:		Discovery of the afterglow and host galaxy of the low redshift short GRB 080905A
Authors:		Rowlinson, A.; Wiersema, K.; Levan, A. J.; Tanvir, N. R.; O'Brien, P. T.; Rol, E.; Hjorth, J.; Thone, C. C.; de Ugarte Postigo, A.;Fynbo, J. P. U.; Jakobsson, P.; Pagani, C.; Stamatikos, M.
Publication:		eprint arXiv:1006.0487
Publication Date:		06/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		Accepted for publication in MNRAS, 10 pages, 5 figures
Bibliographic Code:		2010arXiv1006.0487R

Abstract

We present the discovery of short GRB 080905A, its optical afterglow and host galaxy. Initially discovered by Swift, our deep optical observations enabled the identification of a faint optical afterglow, and subsequently a face-on spiral host galaxy underlying the GRB position, with a chance alignment probability of <1%. There is no supernova component present in the afterglow to deep limits. Spectroscopy of the galaxy provides a redshift of z=0.1218, the lowest redshift yet observed for a short GRB. The GRB lies offset from the host galaxy centre by ~18.5 kpc, in the northern spiral arm which exhibits an older stellar population than the southern arm. No emission lines are visible directly under the burst position, implying little ongoing star formation at the burst location. These properties would naturally be explained were the progenitor of GRB 080905A a compact binary merger.

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Zhao 2010 Fermi-LAT暴的洛仑兹因子

主要内容:
如果低能和高能伽马射线来自同一个区的话，导出的洛仑兹因子会太高。
如果认为他们来自两个不同的区域的话，可以解释观测，不会导致低能段指数下降。

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Title:		The bulk Lorentz factors of Fermi-LAT GRBs
Authors:		Zhao, Xiaohong; Li, Zhuo; Bai, Jinming
Publication:		eprint arXiv:1005.5229
Publication Date:		05/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		6 pages, 5 figures, submitted to ApJ
Bibliographic Code:		2010arXiv1005.5229Z

Abstract

The Lorentz factor (LF) of gamma-ray burst (GRB) ejecta may be constrained by observations of high-energy (HE) spectral attenuation. The recent Fermi-LAT observations of prompt GeV emission from several bright GRBs have leaded to conclusions of unexpectedly large LFs, $\Gamma>10^3$. Here we revisit this problem with two main concerns. (1) With one-zone assumption where all photons are assumed to be generated in the same region (radius) and time, we {\em self-consistently} calculate the $\gamma\gamma$ optical depth by adopting a target photon spectrum with HE cutoff. We find that this might be important when the GRB LF is below a few hundreds. (2) Recent Fermi-LAT observations suggest that the bulk MeV-range and HE ($\ga100$ MeV) emission may arise from different regions. We then consider a two-zone case where HE emission is generated in large radii and mainly attenuated by prompt MeV-range emission generated at small radii. We find that the attenuated HE spectrum does not show an exponential spectral cutoff but a slight steepening. This suggests that there may be no abrupt cutoff due to $\gamma\gamma$ attenuation if relaxing the one-zone assumption. By studying the spectra of three bright Fermi-LAT GRBs 080916C, 090510 and 090902B, we show that a bulk LF of $300\la\Gamma\la600$ can be consistent with observations.

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