[论文解读] Searches for TeV gamma-ray counterparts to Gravitational Wave events with H.E.S.S

H. Ashka, Schüssler, Fabian+1 more|arXiv (Cornell University)|Jun 25, 2019

Gamma-ray bursts and supernovae被引用 4

一句话总结

本研究首次对两个引力波事件——GW170814（双黑洞并合）和GW170817（双中子星并合）——进行了甚高能（VHE）伽马射线后续观测，使用的是H.E.S.S.切伦科夫望远镜阵列。尽管未探测到显著的伽马射线辐射，但该分析建立了针对这些残余物的非热TeV辐射的首份积分上限，为多信使天体物理学模型提供了关键约束。

ABSTRACT

The search for electromagnetic counterparts for gravitational waves events is one of the main topics of multi-messenger Astrophysics. Among these searches is the one for high energy gamma-ray emission with the H.E.S.S. Imaging Atmospheric Cherenkov Telescopes in Namibia. During their second Observation Run O2, the Advanced Virgo detector in Italy and the two advanced LIGO detectors in Washington and Louisiana while conducting joint observations, detected for the first time, on August $14^{th}$, 2017 a transient GW signal due to the coalescence of two stellar masses black holes, an event labeled GW170814. The alert announcing the event was issued two hours later and H.E.S.S. observations could be scheduled for the nights of $16^{th}$, $17^{th}$ and $18^{th}$ August 2017. Three days after the binary BH merger, on August $17^{th}$, the coalescence of two neutron star was detected for the first time, followed by a GRB detection by Fermi's GBM starting a new era in multi-messenger Astronomy. Observations started 5.3 h after the merge and contained the counterpart SSS17a that was identified several hours later. It stands as the first data obtained by a ground-based pointing instrument on this object. In this contribution, we will present the results of the search of high-energy gamma ray emission as electromagnetic counterpart of these two GW events. No significant gamma ray emission was detected for either event. Nevertheless upper limit maps were derived constraining, for the first time, the non-thermal, high-energy emission on the remnant of a three detector binary black hole coalescence (GW170814), and a binary neutron star coalescence (GW170817).

研究动机与目标

• 搜索LIGO与Virgo在O2观测段探测到的引力波事件的甚高能（VHE）伽马射线对应体。
• 利用地面VHE伽马射线望远镜，对双黑洞与双中子星并合残余物的非热辐射进行约束。
• 评估H.E.S.S.阵列在实时响应引力波警报方面的性能与响应效率。
• 为三台探测器参与的双黑洞并合事件（GW170814）与双中子星并合事件（GW170817）提供首份VHE伽马射线上限。

提出的方法

• H.E.S.S.利用其28米望远镜和四台12米望远镜进行后续观测，对50 GeV至100 TeV能量范围内的伽马射线敏感。
• 观测基于LALInference生成的天空位置图安排，通过自动警报处理实现快速响应。
• 数据使用标准的H.E.S.S.分析流程处理，生成显著性图与积分通量上限。
• 在假设通用E⁻²谱型的前提下，针对250 GeV < E < 20 TeV能量范围计算了上限，考虑了角度依赖性与望远镜接受度。
• 尽管最初基于较早、精度较低的位置图进行调度，仍使用GW170814的最终90%可信区域验证了覆盖范围。
• 对于GW170817，H.E.S.S.在LALInference位置图发布后5分钟内完成响应，实现了对中子星并合事件的首次地面VHE观测。

实验结果

研究问题

• RQ1 三台LIGO-Virgo探测器联合探测到的双黑洞并合残余物中，甚高能伽马射线辐射的水平如何？
• RQ2 地面VHE伽马射线望远镜是否能在引力波触发后数分钟内探测到电磁对应体？
• RQ3 对双中子星并合事件的非热TeV辐射，首份积分上限是什么？
• RQ4 H.E.S.S.阵列在最小延迟下，能否高效覆盖引力波事件的定位区域？
• RQ5 引力波定位图中的系统性偏移在多大程度上影响后续观测的灵敏度？

主要发现

• 在对GW170814与GW170817的后续观测中，未探测到显著的VHE伽马射线辐射。
• 对于GW170817，H.E.S.S.在LALInference天空图发布后5分钟内完成响应，实现了对中子星并合事件的首次地面VHE观测。
• 对于GW170814，尽管最初基于精度较低的定位图进行调度，H.E.S.S.观测仍覆盖了最终90%可信区域的约90%。
• 在250 GeV < E < 20 TeV能量范围内，推导出非热辐射的积分上限，这是针对三台探测器参与的双黑洞并合事件的首份此类约束。
• GW170814的上限图提供了对恒星级黑洞双星残余物TeV辐射的首份实证约束。
• GW170817的结果在270 GeV至8.55 TeV范围内设定了严格上限，显著约束了中子星并合非热辐射的模型。