Xin 2010 短暴GRB090426的余辉

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从余辉上看说这个暴可能是大质量恒星坍缩形成的。

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Title:		Probing the Nature of High-z Short GRB 090426 with Its Early Optical and X-ray Afterglows
Authors:		Xin, Liping; Liang, Enwei; Wei, Jianyan; Zhang, Bing; Lv, Houjun; Zheng, Weikang; Urata, Yuji; Im, Myungshin; Wang, Jing; Qiu, Yulei; Deng, Jinsong; Huang, Kuiyun; Hu, Jingyao; Jeon, Yiseul; Li, Huali; Han, Xuhui
Publication:		eprint arXiv:1002.0889
Publication Date:		02/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		7 pages, 1 figures, 2 tables, revised version, MNRAS, in press
Bibliographic Code:		2010arXiv1002.0889X

Abstract

GRB 090426 is a short duration burst detected by Swift ($T_{90}\sim 1.28$ s in the observer frame, and $T_{90}\sim 0.33$ s in the burst frame at $z=2.609$). Its host galaxy properties and some $\gamma$-ray related correlations are analogous to those seen in long duration GRBs, which are believed to be of a massive-star origin (so-called Type II GRBs). We present the results of its early optical observations with the 0.8-m TNT telescope at Xinglong observatory, and the 1-m LOAO telescope at Mt. Lemmon Optical Astronomy Observatory in Arizona. Our well-sampled optical afterglow lightcurve covers from $\sim 90$ seconds to $\sim 10^4$ seconds post the GRB trigger. It shows two shallow decay episodes that are likely due to energy injection, which end at $\sim 230$ seconds and $\sim 7100$ seconds, respectively. The decay slopes post the injection phases are consistent with each other ($\alpha\simeq 1.22$). The X-ray afterglow lightcurve appears to trace the optical, although the second energy injection phase was missed due to visibility constraints introduced by the {\em Swift} orbit. The X-ray spectral index is $\beta_X\sim 1.0$ without temporal evolution. Its decay slope is consistent with the prediction of the forward shock model. Both X-ray and optical emission is consistent with being in the same spectral regime above the cooling frequency ($\nu_c$). The fact that $\nu_c$ is below the optical band from the very early epoch of the observation provides a constraint on the burst environment, which is similar to that seen in classical long duration GRBs. We therefore suggest that death of a massive star is the possible progenitor of this short burst.

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