We present the radio afterglow of short gamma-ray burst (GRB) 230217A, which was detected less than 1 day after the gamma-ray prompt emission with the Australia Telescope Compact Array (ATCA) and the Karl G. Jansky Very Large Array. The ATCA rapid-response system automatically triggered an observation of GRB 230217A following its detection by the Neil Gehrels Swift Observatory and began observing the event just 32 minutes postburst at 5.5 and 9 GHz for 7 hr. Dividing the 7 hr observation into three time-binned images allowed us to obtain radio detections with logarithmic central times of 1, 2.8, and 5.2 hr postburst, the first of which represents the earliest radio detection of any GRB to date. The decline of the light curve is consistent with reverse shock emission if the observing bands are below the spectral peak and not affected by synchrotron self-absorption. This makes GRB 230217A the fifth short GRB (SGRB) with radio detections attributed to a reverse shock at early times (<1 day postburst). Following brightness temperature arguments, we have used our early radio detections to place the highest minimum Lorentz factor ( Γmin>50 at ∼1 hr) constraints on a GRB in the radio band. Our results demonstrate the importance of rapid radio follow-up observations with long integrations and good sensitivity for detecting the fast-evolving radio emission from SGRBs and probing their reverse shocks.

中文翻译：

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短 GRB 230217A 的早期射电余辉


我们介绍了短伽马射线暴 （GRB） 230217A 的射电余辉，该余辉是在伽马射线瞬发发射后不到 1 天用澳大利亚望远镜紧凑型阵列 （ATCA） 和 Karl G. Jansky 甚大阵列探测到的。ATCA 快速响应系统在 Neil Gehrels Swift 天文台检测到 GRB 230217A 后自动触发了对它的观测，并在 5.5 GHz 和 9 GHz 爆发后仅 32 分钟就开始观测该事件，持续 7 小时。将 7 小时的观测分为三个时间分箱图像，使我们能够获得对数中心时间为 1、2.8 和 5.2 小时后爆发的射电探测，其中第一个代表了迄今为止对任何 GRB 的最早射电探测。如果观测波段低于光谱峰值且不受同步加速器自吸收的影响，则光曲线的下降与反向冲击发射一致。这使得 GRB 230217A 成为第五个短 GRB （SGRB），其无线电探测归因于早期（爆发后 <1 天）的反向冲击。根据亮温参数，我们使用早期的无线电探测对无线电频段中的 GRB 施加了最高的最小洛伦兹因子（∼1 hr 时的 Γmin>50）约束。我们的结果表明，具有长积分和良好灵敏度的快速射电跟踪观测对于检测 SGRB 快速演变的射电发射并探测其反向冲击的重要性。