A correlation between the intrinsic brightness and average decay rate of Swift /UVOT gamma-ray burst optical/ultraviolet light curves

We examine a sample of 48 Swift /UVOT long gamma-ray burst light curves and find a correlation between the logarithmic luminosity at 200 s and average decay rate determined from 200 s onwards, with a Spearman rank coefficient of − 0.58 at a significance of 99.998 per cent (4.2 σ ). We discuss the causes of the log L 200s – α > 200s correlation, finding it to be an intrinsic property of long gamma-ray bursts, and not resulting from the selection criteria. We find two ways to produce the correlation. One possibility is that there is some property of the central engine, outflow or external medium that affects the rate of energy release so that the bright afterglows release their energy more quickly and decay faster than the fainter afterglows. Alternatively, the correlation may be produced by variation of the observer’s viewing angle, with observers at large viewing angles observing fainter and slower decaying light curves.

我们研究了48个雨燕卫星/紫外/光学望远镜（Swift/UVOT）长伽马射线暴光变曲线的样本，发现200秒时的对数光度与从200秒起确定的平均衰减率之间存在相关性，斯皮尔曼等级系数为 - 0.58，显著性为99.998%（4.2倍标准差）。我们讨论了log L₂₀₀ₛ - α>₂₀₀ₛ相关性的成因，发现它是长伽马射线暴的一种固有属性，并非由选择标准导致。我们发现了产生这种相关性的两种方式。一种可能性是，中心引擎、喷流或外部介质存在某些特性，影响能量释放速率，使得明亮的余辉比暗淡的余辉更快地释放能量且衰减得更快。另一种可能性是，这种相关性可能是由观测者视角的变化产生的，大视角的观测者观测到的光变曲线更暗且衰减更慢。