Here we present stringent low-frequency (185 MHz) limits on coherent radio emission associated with a short-duration gamma-ray burst (SGRB). Our observations of the short gamma-ray burst (GRB) 180805A were taken with the upgraded Murchison Widefield Array (MWA) rapid-response system, which triggered within 20s of receiving the transient alert from the Swift Burst Alert Telescope, corresponding to 83.7 s post-burst. The SGRB was observed for a total of 30 min, resulting in a $3\sigma$ persistent flux density upper limit of 40.2 mJy beam–1. Transient searches were conducted at the Swift position of this GRB on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in $3\sigma$ limits of 570–1 830, 270–630, 200–420, and 100–200 mJy beam–1, respectively. We also performed a dedispersion search for prompt signals at the position of the SGRB with a temporal and spectral resolution of 0.5 s and 1.28 MHz, respectively, resulting in a $6\sigma$ fluence upper-limit range from 570 Jy ms at DM $=3\,000$ pc cm–3 ( $z\sim 2.5$ ) to 1 750 Jy ms at DM $=200$ pc cm–3 ( $z\sim 0.1)$ , corresponding to the known redshift range of SGRBs. We compare the fluence prompt emission limit and the persistent upper limit to SGRB coherent emission models assuming the merger resulted in a stable magnetar remnant. Our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ISM) or persistent pulsar-like emission from the spin-down of the magnetar. However, in the case of a more powerful SGRB (a gamma-ray fluence an order of magnitude higher than GRB 180805A and/or a brighter X-ray counterpart), our MWA observations may be sensitive enough to detect coherent radio emission from the jet-ISM interaction and/or the magnetar remnant. Finally, we demonstrate that of all current low- frequency radio telescopes, only the MWA has the sensitivity and response times capable of probing prompt emission models associated with the initial SGRB merger event.

中文翻译：

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Murchison Widefield Array 对短 GRB 180805A 的快速响应观测

在这里，我们对与短时伽马射线爆发 (SGRB) 相关的相干无线电发射提出了严格的低频 (185 MHz) 限制。我们对短伽马射线暴 (GRB) 180805A 的观测是使用升级后的默奇森宽场阵列 (MWA) 快速响应系统进行的，该系统在收到来自迅速爆发警报望远镜，对应于爆发后 83.7 秒。短暴共被观察了 30 分钟，导致 $3\sigma$ 40.2 mJy 光束的持续通量密度上限–1. 瞬态搜索在迅速该 GRB 在 0.5 秒、5 秒、30 秒和 2 分钟时间尺度上的位置，导致 $3\sigma$ 570–1 830、270–630、200–420 和 100–200 mJy 光束的限制–1， 分别。我们还对短暴位置的瞬态信号进行了去色散搜索，时间和光谱分辨率分别为 0.5 s 和 1.28 MHz，得到 $6\sigma$ 通量上限范围从 570 Jy ms at DM $=3\,000$ 个厘米–3( $z\sim 2.5$ ) 到 1 750 Jy ms 在 DM $=200$ 个厘米–3( $z\sim 0.1)$ ，对应于已知的短暴红移范围。假设合并导致稳定的磁星残余，我们将注量即时发射极限和持续上限与短暴相干发射模型进行了比较。我们的观测不够灵敏，无法检测到与合并之前双中子星磁场排列相关的即时发射，来自相对论射流与星际介质（ISM）之间的相互作用或来自磁星减速。然而，对于更强大的短暴（伽马射线通量比 GRB 180805A 高一个数量级和/或更亮的 X 射线对应物），我们的 MWA 观测可能足够灵敏，可以检测到来自喷流的相干无线电发射-ISM 相互作用和/或磁星残余。最后，