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A Late-time Radio Survey of Short Gamma-ray Bursts at z < 0.5: New Constraints on the Remnants of Neutron-star Mergers
The Astrophysical Journal ( IF 4.9 ) Pub Date : 2020-10-14 , DOI: 10.3847/1538-4357/abb407
Genevieve Schroeder 1 , Ben Margalit 2 , Wen-fai Fong 1 , Brian D. Metzger 3, 4 , Peter K. G. Williams 5, 6 , Kerry Paterson 1 , Kate D. Alexander 1 , Tanmoy Laskar 7 , Armaan V. Goyal 1 , Edo Berger 5
Affiliation  

Massive, rapidly-spinning magnetar remnants produced as a result of binary neutron star (BNS) mergers may deposit a fraction of their energy into the surrounding kilonova ejecta, powering a synchrotron radio signal from the interaction of the ejecta with the circumburst medium. We present 6.0 GHz Very Large Array (VLA) observations of nine, low-redshift short gamma-ray bursts (SGRBs; $z<0.5$) on rest-frame timescales of $\approx2.4-13.9$ yr following the bursts. We place $3\sigma$ limits on radio continuum emission of $F_{\nu}\lesssim6-20\,\mu$Jy at the burst positions, or $L_{\nu}\lesssim(0.6-8.3)\times10^{28}$erg s$^{-1}$Hz$^{-1}$. Comparing these limits with new light curve modeling which properly incorporates relativistic effects, we obtain limits on the energy deposited into the ejecta of $E_{ej}\lesssim(0.6-6.7)\times 10^{52}$erg ($E_{ej}\lesssim(1.8-17.6)\times10^{52}$erg) for an ejecta mass of $0.03\,M_{\odot}$ ($0.1\,M_{\odot}$). We present a uniform re-analysis of 27 SGRBs with $5.5-6.0$ GHz observations, and find that $\gtrsim50\%$ of SGRBs did not form stable magnetar remnants in their mergers. Assuming SGRBs are produced by BNS mergers drawn from the Galactic BNS population plus an additional component of high-mass GW194025-like mergers in a fraction $f_{GW190425}$ of cases, we place constraints on the maximum mass of a non-rotating neutron star (NS) ($M_{TOV}$), finding $M_{TOV}\lesssim2.23\,M_{\odot}$ for $f_{GW190425}=0.4$; this limit increases for larger values of $f_{GW190425}$. The detection (or lack thereof) of radio remnants in untargeted surveys such as the VLA Sky Survey (VLASS) could provide more stringent constraints on the fraction of mergers that produce stable remnants. If $\gtrsim30-300$ radio remnants are discovered in VLASS, this suggests that SGRBs are a biased population of BNS mergers in terms of the stability of the remnants they produce.

中文翻译:

对 z < 0.5 处短伽马射线暴的后期射电调查:中子星合并残余的新约束

由双中子星 (BNS) 合并产生的巨大、快速旋转的磁星残余物可能会将它们的一小部分能量沉积到周围的千新星喷射物中,从而为喷射物与环绕暴介质相互作用产生的同步加速器无线电信号提供动力。我们展示了 6.0 GHz 甚大阵列 (VLA) 对九次低红移短伽马射线暴(SGRB;$z<0.5$)在暴发后每年 $\approx2.4-13.9$ 的静止帧时间尺度上的观测结果。我们将 $3\sigma$ 限制在 $F_{\nu}\lesssim6-20\,\mu$Jy 的射电连续谱发射位置,或 $L_{\nu}\lesssim(0.6-8.3)\times10^ {28}$erg s$^{-1}$Hz$^{-1}$。将这些限制与正确结合相对论效应的新光曲线模型进行比较,我们获得了沉积到 $E_{ej}\lesssim(0.6-6. 7)\times 10^{52}$erg ($E_{ej}\lesssim(1.8-17.6)\times10^{52}$erg) 对于喷射质量为 $0.03\,M_{\odot}$ ($0.1\ ,M_{\odot}$)。我们对 5.5-6.0$ GHz 观测值的 27 个短暴进行了统一的重新分析,发现 $\gtrsim50\%$ 的短暴在合并中没有形成稳定的磁星残余。假设短暴是由从银河 BNS 群体中抽取的 BNS 合并产生的,加上在 $f_{GW190425}$ 的一小部分情况下的大质量 GW194025 类合并的额外组成部分,我们对非旋转中子的最大质量进行了限制star (NS) ($M_{TOV}$),找到 $M_{TOV}\lesssim2.23\,M_{\odot}$ 为 $f_{GW190425}=0.4$;对于较大的 $f_{GW190425}$ 值,此限制会增加。在诸如 VLA 巡天 (VLASS) 之类的无目标勘测中检测(或缺乏)无线电残余可以对产生稳定残余的合并比例提供更严格的限制。如果在 VLASS 中发现了 $\gtrsim30-300$ 无线电残余,这表明就它们产生的残余的稳定性而言,短暴是 BNS 合并的有偏见的群体。
更新日期:2020-10-14
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