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arXiv 1907.01889astro-ph.HE
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当伽马射线暴余辉首次进入雨燕紫外线和光学望远镜视野时的研究

A study of gamma-ray burst afterglows as they first come into view of the Swift Ultraviolet and Optical Telescope

M. J. Page, S. R. Oates, M. De Pasquale, A. A. Breeveld, S. W. K. Emery, N. P. M. Kuin, F. E. Marshall, M. H. Siegel, P. W. A. Roming

摘要:

我们研究了来自光学明亮的伽马射线暴(GRB)余辉的发射,因为尼尔·盖尔斯斯威夫特天文台的紫外线和光学望远镜(UVOT)首先开始观测,之后转向瞄准GRB,而斯威夫特卫星的指向仍在解决。我们验证的测光质量的UVOT沉降数据使用明亮的恒星在视野中。在大多数情况下,我们发现没有问题的解决曝光测光,但在一种情况下,我们切除曝光的第一秒,以减轻航天器的姿态重建问题,在第二种情况下,我们排除了第一秒的曝光,其中UVOT光阴极电压似乎是斜升。在23个余辉的样本中,峰值V幅度<16,我们发现,当雨燕到达目标时,所有的余辉都在稳定曝光中被检测到。对于9个伽玛暴的UVOT解决曝光发生在提示伽玛射线发射的结论。其中五个伽玛暴在稳定曝光后具有明确的光学峰,其光学光变曲线上升>0.5 mag,并且这些伽玛暴有长T90的边缘趋势。这种趋势是预期厚壳余辉,但时间指数的光学上升和光学峰值的时间似乎排除厚壳。

英文摘要:

We examine the the emission from optically bright gamma-ray burst (GRB) afterglows as the Ultraviolet and Optical Telescope (UVOT) on the Neil Gehrels Swift Observatory first begins observing, following the slew to target the GRB, while the pointing of the Swift satellite is still settling. We verify the photometric quality of the UVOT settling data using bright stars in the field of view. In the majority of cases we find no problems with the settling exposure photometry, but in one case we excise the first second of the exposure to mitigate a spacecraft attitude reconstruction issue, and in a second case we exclude the first second of the exposure in which the UVOT photocathode voltage appears to be ramping up. Of a sample of 23 afterglows which have peak V magnitudes <16, we find that all are detected in the settling exposures, when Swift arrives on target. For 9 of the GRBs the UVOT settling exposure took place before the conclusion of the prompt gamma-ray emission. Five of these GRBs have well defined optical peaks after the settling exposures, with rises of >0.5 mag in their optical lightcurves, and there is a marginal trend for these GRBs to have long T90. Such a trend is expected for thick-shell afterglows, but the temporal indices of the optical rises and the timing of the optical peaks appear to rule out thick shells.

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