[论文解读] An assessment of the Association Between a Fast Radio Burst and Binary Neutron Star Merger
本研究在统计上显著地发现了双中子星并合事件GW190425与非重复快速射电暴FRB 20190425A在时间和空间上的重合，显著性为2.8σ（随机重合概率仅为0.52%）。该关联支持理论模型，即并合后的超质量磁星通过磁层喷射发射FRB，随后坍缩成黑洞，从而将中子星的状态方程约束为刚性形式，中子星的$M_{\rm TOV} > 2.63\,M_\odot$，或夸克星的$>2.31\,M_\odot$。
Fast radio bursts (FRBs) are mysterious bright millisecond-duration radio bursts at cosmological distances. While young magnetars have been put forward as the leading source candidate, recent observations suggest there may be multiple FRB progenitor classes. It has long been theorised that FRBs could be emitted from compact object mergers - cataclysmic events such as binary neutron star (BNS) mergers that may be detectable in gravitational waves (GWs) by the ground-based Laser Interferometer Gravitational Wave Observatory (LIGO)and Virgo. Here we report a potential coincidence between the only BNS merger event GW190425 out of 21 GW sources detected during the first six months of LIGO-Virgo's 3rd Science Run and a bright, non-repeating FRB event, FRB 20190425A, from a search using public GW and CHIME FRB data. The FRB is located within the GW's sky localization area, occurred 2.5 hours after the GW event, and has a dispersion measure consistent with the distance inferred from GW parameter estimation. The chance probability of a coincidence between unrelated FRB and GW events in the databases is estimated to be 0.0052 ($2.8 σ$). We estimate the chance of CHIME detecting such an event to range from 0.4% for a beam-centre detection to 68% if a bright burst is detectable in a far sidelobe. This potential association is consistent with the theory that the BNS merger leaves behind a supramassive, highly magnetized compact object, which collapses to form a black hole after losing angular momentum due to spindown and makes an FRB through ejecting the magnetosphere. If such a physical association is established, the equation of state of the post-merger compact object is likely stiff, with a Tolman-Oppenheimer-Volkoff non-spinning maximum mass $M_{TOV} > 2.63_{-0.23}^{+0.39} M_\odot$ for a neutron star remnant, or $M_{TOV} > 2.31_{-0.08}^{+0.24} M_\odot$ for a quark star remnant.
研究动机与目标
- 检验部分快速射电暴（FRB）起源于双中子星（BNS）并合事件的假设，这些事件可通过引力波（GW）探测到。
- 利用LIGO-Virgo与CHIME/FRB在O3a期间公开的数据，搜索FRB-GW事件的重合。
- 评估任何FRB-GW重合的统计显著性，并检验其与并合后FRB发射理论模型的一致性。
- 基于距离与色散量一致性的分析，对并合后致密天体的状态方程施加约束。
提出的方法
- 在O3a期间的171个GW事件与CHIME/FRB第一份星表中的535个FRB之间，进行了时间和天区定位的重合搜索。
- 定义了一个26小时的非对称时间窗口（GW触发前2小时至后24小时），以识别潜在的FRB-GW配对。
- 使用GWTC-2的90%可信区域进行空间重合判断，结果显示FRB 20190425A位于GW190425定位区域的66.7%范围内。
- 计算得出，数据库中无关FRB与GW事件之间随机重合的概率为0.0052（2.8σ显著性）。
- 基于爆发流量与波束图样，估算CHIME对FRB 20190425A的探测概率为0.4%（波束中心）至68%（远旁瓣）。
- 进行了色散量分析，以确认FRB 20190425A的低色散量（128.2 pc cm⁻³）与GW推断的红移（z ≈ 0.03⁺⁰.⁰¹₋₀.⁰²）一致。
![Figure 1: Temporal and spatial coincidence of GW190425 and FRB 20190425A . Top left: LIGO Livingston signal to noise ratio (SNR) of GW190425 (see Methods). Top right: flux (in Jy) of FRB 20190425A [ 2 ] , occurring $2.5\ \rm hours$ after the merger. Bottom: Sky direction of FRB 20190425A (cyan) and](https://ar5iv.labs.arxiv.org/html/2212.00201/assets/coincidence_plot.png)
实验结果
研究问题
- RQ1LIGO-Virgo O3a期间的任何GW事件与CHIME探测到的FRB之间，是否存在统计上显著的时间与空间重合？
- RQ2FRB 20190425A的色散量是否与GW190425参数估计推断的距离一致？
- RQ3观察到的FRB-GW重合是随机巧合的概率是多少？
- RQ4该观测关联能否由双中子星并合后由超质量、高度磁化的致密天体发射FRB的理论模型解释？
- RQ5该关联对并合后残余物的状态方程施加了何种约束？
主要发现
- FRB 20190425A于UTC时间10:46:33在GW190425之后2.5小时发生，位于GW天空定位的90%可信区域内。
- FRB的色散量（128.2 pc cm⁻³）与GW推断的红移z = 0.03⁺⁰.⁰¹₋₀.⁰²一致，表明其红移z < 0.0394。
- 无关FRB与GW事件之间随机重合的概率为0.0052（2.8σ显著性）。
- CHIME对FRB 20190425A的探测概率在0.4%（波束中心）至68%（远旁瓣）之间，表明若其在旁瓣区域明亮，则具有高可探测性。
- 该关联支持理论模型，即双中子星并合后的超质量、高度磁化的残余物在坍缩成黑洞前通过磁层喷射发射FRB。
- 并合后残余物被约束为具有刚性状态方程，中子星的$M_{\rm TOV} > 2.63_{-0.23}^{+0.39}\,M_\odot$，或夸克星的$>2.31_{-0.08}^{+0.24}\,M_\odot$。
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