标题： 短硬伽马射线暴的星系宿主和大尺度环境 显示英文标题

标题： The Galaxy Hosts and Large-Scale Environments of Short-Hard Gamma-Ray Bursts

摘要： 短伽马射线暴（GRBs）的迅速发现使人们对爆炸的能量学及前身星的性质有了前所未有的认识。然而，在没有检测到明确证据（如引力波爆发或Li-Paczynski微型超新星）之前，很难对前身星做出确定的结论。与长软谱GRBs的情况类似，人们期望通过对短伽马射线暴宿主及其位置的系统研究能够开始揭示它们的本质。我们首次对短硬谱GRBs的宿主星系进行了综合研究。具体而言，我们展示了三个短伽马射线暴宿主星系的Gemini-North和Keck发现光谱，以及第四个宿主星系的中等分辨率（R~6000）光谱。我们发现这些短硬谱GRBs起源于多种低红移（z<1）环境，这些环境与长软谱GRBs的环境在单个星系尺度和星系团尺度上都有显著差异。具体来说，三个爆发事件被发现与没有当前（<0.1 Msol/hr）或近期恒星形成的老且质量大的星系有关。其中两个星系位于一个星团环境中。这些观测结果支持了短硬谱GRBs起源于致密星残骸合并（如双中子星或中子星-黑洞双星）的观点。相比之下，第四次事件发生在恒星形成率超过0.5 Msol/yr的小星系中。因此，似乎短硬谱爆发的前身星就像Ia型超新星一样，在所有类型的星系中都存在，这表明相应的一类具有从形成到爆炸之间广泛的延迟时间分布。 显示英文摘要

摘要： The rapid succession of discovery of short--duration hard--spectrum GRBs has led to unprecedented insights into the energetics of the explosion and nature of the progenitors. Yet short of the detection of a smoking gun, like a burst of coincident gravitational radiation or a Li-Paczynski mini-supernova, it is unlikely that a definitive claim can be made for the progenitors. As was the case with long--duration soft--spectrum GRBs, however, the expectation is that a systematic study of the hosts and the locations of short GRBs could begin to yield fundamental clues about their nature. We present the first aggregate study of the host galaxies of short--duration hard--spectrum GRBs. In particular, we present the Gemini--North and Keck discovery spectra of the galaxies that hosted three short GRBs and a moderate--resolution (R~6000) spectrum of a fourth host. We find that these short--hard GRBs originate in a variety of low-redshift (z<1) environments that differ substantially from those of long--soft GRBs, both on individual galaxy scales and on galaxy--cluster scales. Specifically, three of the bursts are found to be associated with old and massive galaxies with no current (< 0.1 Msol/hr) or recent star formation. Two of these galaxies are located within a cluster environment. These observations support an origin from the merger of compact stellar remnants, such as double neutron stars of a neutron star--black hole binary. The fourth event, in contrast, occurred within a dwarf galaxy with a star formation rate exceeding 0.5 Msol/yr. Therefore, it appears that like supernovae of Type Ia, the progenitors of short--hard bursts are created in all galaxy types, suggesting a corresponding class with a wide distribution of delay times between formation and explosion.