[论文解读] The Progenitors of Short-Hard Gamma-Ray Bursts from an Extended Sample of Events

A. Gal‐Yam, Ehud Nakar+12 more|Sep 29, 2005

Gamma-ray bursts and supernovae参考文献 8被引用 16

一句话总结

本研究通过光学和X射线观测，扩展了已知宿主星系或红移的短时延长伽马射线暴（SHBs）样本，识别出两个新的可能宿主，并确认SHB前身体的典型年龄通常长于Ia型超新星的前身体，中位寿命达数十亿年。研究结果挑战了标准的中子星并合模型（该模型预测延迟时间较短），并表明SHBs主要宿主为老年恒星种群，倾向于中等红移的星系团。

ABSTRACT

The detection of the afterglow emission and host galaxies of short-hard gamma-ray bursts (SHBs) is one of the most exciting recent astronomical discoveries. Indications that SHB progenitors belong to old stellar populations, in contrast to those of the long-soft GRBs, provide a strong clue about their physical nature. Definitive conclusions however are limited by the small number of SHBs with known hosts. Here, we present our investigation of SHBs previously localized by the interplanetary network (IPN) using new and archival optical and X-ray observations. We show that we can likely identify the host galaxies/clusters for additional two bursts, significantly increasing the sample of SHBs with known hosts and/or distances. In particular, we determine that the bright SHB 790613 occurred within the rich galaxy cluster Abell 1892, making it probably the nearest SHB currently known. We show that the brightest galaxy within the error box of SHB 000607, at z=0.14, is most likely the host galaxy of this event. Additionally, we rule out the existence of galaxy overdensities (down to ~21mag) near the locations of two other SHBs, and set a lower limit on their probable redshift. We combine our SHB sample with events discovered recently by the Swift and HETE-2 missions, and investigate the properties of the extended sample. Comparison to SNe Ia shows that the progenitors of SHBs are typically older, implying a typical life time of several Gy. We also show that it is unlikely that there is a significant population of progenitors with life time shorter than 1Gy. This result disfavors the popular model of NS-NS mergers as the progenitors of SHBs.

研究动机与目标

• 通过有限的先前定位信息，识别并确认短时延长伽马射线暴（SHBs）的宿主星系或宿主星系团。
• 通过分析宿主星系类型和红移，确定SHBs的典型前身体年龄。
• 根据观测约束，检验中子星并合模型作为SHB前身体的可行性。
• 评估长前身体寿命对SHB红移分布及引力波对应体可探测性的影响。

提出的方法

• 利用新的和档案的光学与X射线观测，在SHBs的星际网络（IPN）误差框内搜索宿主星系或星系团。
• 应用统计分析评估宿主星系关联的可能性，包括红移匹配和检测到星系过密区域（最低至r ≈ 21等）。
• 将扩展的SHB样本与Swift和HETE-2事件结合，分析宿主星系类型和红移分布。
• 通过未检测到明显星系过密区域，计算缺乏明确宿主关联的SHBs的红移下限。
• 将观测到的SHB红移和宿主类型分布与中子星并合模型及恒星形成历史的预测进行比较。
• 使用分层星系形成模型，解释在中等红移下对星系团环境的偏好。

实验结果

研究问题

• RQ1 基于宿主星系特性与红移，SHB前身体的典型年龄是多少？
• RQ2 能否通过多波段后续观测识别出此前未定位的SHBs的宿主星系或星系团？
• RQ3 中子星并合模型是否与观测到的SHB红移和宿主星系类型分布一致？
• RQ4 长前身体寿命对预期SHB红移分布和聚类特性有何影响？
• RQ5 本地SHB发生率与以往估计相比如何？这对引力波探测意味着什么？

主要发现

• 明亮SHB 790613极有可能发生在富星系团Abell 1892内，使其成为目前已知最近的SHB，红移z ≈ 0.1405。
• SHB 000607在z = 0.1405的误差框内最亮星系极有可能是其宿主，经高统计显著性确认。
• SHB的前身体通常比Ia型超新星的前身体更老，中位寿命达数十亿年，与约10亿年的短延迟时间预测不一致。
• 观测到的SHB红移分布与标准中子星并合模型不一致，后者预测存在大量寿命短暂的前身体。
• 样本表明，红移z ≈ 0.5以上的SHBs应主要发生在星系团中，因为那里的老年恒星种群更为集中。
• 本地SHB发生率估计为>10 Gpc⁻³ yr⁻¹，显著高于以往估计，提升了先进LIGO探测引力波的可能性。