astro-grb

Liping Xin, Enwei Liang, Jianyan Wei, Bing Zhang, Houjun Lv, Weikang Zheng, Yuji Urata, Myungshin Im, Jing Wang, Yulei Qiu, Jinsong Deng, Kuiyun Huang, Jingyao Hu, Yiseul Jeon, Huali Li, Xuhui Han

Swift GRB 090426 is a short duration burst T_{90}~0.33 seconds in the burst
frame at z=2.609) with analogous properties on its host galaxy and
spectrum-energy correlation to typical long duration GRBs from collapses of
massive stars (Type II GRBs). We present its early optical observations with
0.8-m TNT telescope at Xinglong observatory and 1-m telescope at Mt. Lemmon
Optical Astronomy Observatory LOAO in Arizona. Our well-sampled optical
afterglow lightcurve covered from ~90 seconds to ~10^4 seconds post the GRB
trigger shows two energy injection phases ended at ~230 seconds and ~7100
seconds, respectively. The decay slopes post the injection phases are
consistent with each other (\alpha ~1.22). The X-ray afterglow lightcurve seems
to trace the optical one, although the second energy injection phase was missed
due to the orbit constrain of Swift satellite. The spectral index of the X-rays
is ~1.0 without temporal evolution. The X-ray emission is consistent with the
forward shock models. Both the X-ray and optical emission would be in the same
spectral regime above the cooling frequency (\nu_c). The fact that the \nu_c is
below the optical bands since a very early epoch constrains the burst in a
medium environment similar to typical Type II GRBs, hence suggests the death of
a massive star as a possible progenitor of this burst.

http://arxiv.org/abs/1002.0889