探测具有时间变化性的PDKEEPAAA环境：GRB 080210的ULTRASPEC快速成像
Probing GRB environments with time variability: ULTRASPEC fast imaging of GRB 080210
摘要：
我们提出了高时间分辨率（1.09秒）测光的GRB 080210获得ULTRASPEC安装在ESO/3.6米望远镜，开始68.22分钟后爆发，持续26.45分钟。光变曲线是平滑的短（下降到2.18秒）和长的时间尺度，证实了一个无特征的功率谱。在火球幂律衰减的顶部，原则上，不同时间尺度的颠簸和摆动可以由环爆介质中的密度波动、射流中的子结构或刷新的冲击产生。比较我们的约束条件与来自运动学参数的变率限制，我们排除了在时间尺度\Deltat > 9.2分钟（2%的\Deltat > 2.3分钟的许多波动区域）下产生通量下降大于1%的密度波动。此外，我们还研究了余辉VLT/FORS 2谱、光-X射线谱能量分布（SED）和时间衰减。SED最符合破幂律，斜率βopt = 0.71 \pm 0.01和βX = 1.59 \pm 0.07，与火球模型不一致，表明GRB 080210存在非标准余辉。我们发现AV = 0.18 \pm 0.03 MAG的光学消光由于SMC类尘埃和过量的X射线吸收log（NH/cm-2）= 21.58 +0.18 -0.26假设太阳丰度。光谱分析表明，Lyα吸收体（log（NH I /cm-2）= 21.90 \pm 0.10）具有低金属丰度（[X/H] = -1.21 \pm 0.16），可能与GRB宿主星系（z = 2.641）的星际介质有关。
英文摘要：
We present high time resolution (1.09 s) photometry of GRB 080210 obtained with ULTRASPEC mounted on the ESO/3.6-m telescope, starting 68.22 min after the burst and lasting for 26.45 min. The light curve is smooth on both short (down to 2.18 s) and long time scales, confirmed by a featureless power spectrum. On top of the fireball power-law decay, bumps and wiggles at different time scales can, in principle, be produced by density fluctuations in the circumburst medium, substructures in the jet or by refreshed shocks. Comparing our constraints with variability limits derived from kinematic arguments, we exclude under-density fluctuations producing flux dips larger than 1 per cent with time scales \Deltat > 9.2 min (2 per cent on \Deltat > 2.3 min for many fluctuating regions). In addition, we study the afterglow VLT/FORS2 spectrum, the optical-to-X-ray spectral energy distribution (SED) and the time decay. The SED is best fit with a broken power law with slopes βopt = 0.71 \pm 0.01 and βX = 1.59 \pm 0.07, in disagreement with the fireball model, suggesting a non-standard afterglow for GRB 080210. We find AV = 0.18 \pm 0.03 mag optical extinction due to SMC-like dust and an excess X-ray absorption of log (NH/cm-2) = 21.58 +0.18 -0.26 assuming Solar abundances. The spectral analysis reveals a damped Lyα absorber (log (NH I /cm-2) = 21.90 \pm 0.10) with a low metallicity ([X/H] = -1.21 \pm 0.16), likely associated with the interstellar medium of the GRB host galaxy (z = 2.641).
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