三个短/硬伽马射线暴的光学余辉和宿主星系
The optical afterglows and host galaxies of three short/hard gamma-ray bursts
摘要：
短伽玛暴通常被认为起源于双致密天体双星的合并，但这种情况的直接证据仍然缺失。短伽玛暴的光学观测使我们能够测量红移，确定宿主星系，描述它们的性质，并准确地定位伽玛暴。对伽玛暴余辉的多波长观测提供了有关工作中的辐射机制的有用信息。这些都是关键问题，使人们能够区分这些难以捉摸的事件的不同模型。我们用ESO-VLT对短/硬GRB 051227、GRB 061006和GRB 071227进行了测光观测，从爆炸后几小时开始，一直到几天后的宿主星系水平。对于GRB 061006和GRB 071227，我们还获得了宿主星系的光谱观测。我们比较了我们的光学观测结果与现有的X射线数据，这些爆发。对于上述三次爆发，我们都发现了光学余辉，并确定了它们的宿主星系。在爆发后大约半天，GRB 051227和GRB 061006的光学余辉呈现出比X射线更陡峭的衰减。在GRB 051227的情况下，光学衰减是如此陡峭，它可能表明在两个波长范围内的不同发射机制。这三个宿主是蓝色的恒星形成星系，红移适中，金属丰度与太阳相当。光学余辉从其宿主星系中心的投影偏移范围很广，但所有的余辉都位于其宿主星系的光中，并在其X射线光谱中提供了局部吸收的证据。我们讨论了我们的研究结果，根据目前的模型短GRB祖细胞。
英文摘要：
Short GRBs are commonly thought to originate from the merging of double compact object binaries but direct evidence for this scenario is still missing. Optical observations of short GRBs allow us to measure redshifts, firmly identify host galaxies, characterize their properties, and accurately localize GRBs within them. Multiwavelength observations of GRB afterglows provide useful information on the emission mechanisms at work. These are all key issues that allow one to discriminate among different models of these elusive events. We carried out photometric observations of the short/hard GRB 051227, GRB 061006, and GRB 071227 with the ESO-VLT starting from several hours after the explosion down to the host galaxy level several days later. For GRB 061006 and GRB 071227 we also obtained spectroscopic observations of the host galaxy. We compared the results obtained from our optical observations with the available X-ray data of these bursts. For all the three above bursts, we discovered optical afterglows and firmly identified their host galaxies. About half a day after the burst, the optical afterglows of GRB 051227 and GRB 061006 present a decay significatly steeper than in the X-rays. In the case of GRB 051227, the optical decay is so steep that it likely indicates different emission mechanisms in the two wavelengths ranges. The three hosts are blue, star forming galaxies at moderate redshifts and with metallicities comparable to the Solar one. The projected offsets of the optical afterglows from their host galaxies centers span a wide range, but all afterglows lie within the light of their hosts and present evidence for local absorption in their X-ray spectra. We discuss our findings in light of the current models of short GRB progenitors.
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