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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 Year :
2010

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.<br />Comment: 7 pages, 1 figures, 2 tables, revised version, MNRAS, in press

Details

Database :
arXiv
Publication Type :
Report
Accession number :
edsarx.1002.0889
Document Type :
Working Paper
Full Text :
https://doi.org/10.1111/j.1365-2966.2010.17419.x