论文标题
短伽玛射线爆发的Circumburst环境的限制
Constraints on the circumburst environments of short gamma-ray bursts
论文作者
论文摘要
局部良好的短伽马射线爆发（SGRB）的观察性随访剩下的$ 20-30 \％的人口，没有重合的寄主银河系协会到深度光学和NIR限制（$ \ gtrsim 26 $ mag）。这些SGRB由于缺乏强大的宿主关联而被归类为无观察宿主。有人认为，这些无宿主的SGRB可能表明二进制中子星系（由于出生的踢）在其形成与合并之间（导致SGRB）所穿越的大距离。周围的Circumburst密度可以间接探测GRB从其宿主星系的距离。我们表明，这些密度可以从早期的余辉灯弯曲中获得。我们发现我们的样本中的$ \ lyssim16 \％$ $是在密度$ \ lyssim10^{ - 4} $ cm $^{ - 3} $的情况下进行的。这些密度代表距离的预期值大于宿主星系的病毒半径。我们发现，在我们样本中发现的五个SGRB中，发现在宿主上是无宿主的，没有一个与出生星系的病毒半径之外发生的相一致。这意味着两种情况之一。要么这些无观察的无宿主SGRB出现在其宿主星系半径之外，但在银河系的光环中，或者在中等至高红移（$ z \ gtrsim 2 $）的宿主星系中被随访观察所遗漏。
Observational follow-up of well localized short gamma-ray bursts (SGRBs) has left $20-30\%$ of the population without a coincident host galaxy association to deep optical and NIR limits ($\gtrsim 26$ mag). These SGRBs have been classified as observationally hostless due to their lack of strong host associations. It has been argued that these hostless SGRBs could be an indication of the large distances traversed by the binary neutron star system (due to natal kicks) between its formation and its merger (leading to a SGRB). The distances of GRBs from their host galaxies can be indirectly probed by the surrounding circumburst densities. We show that a lower limit on those densities can be obtained from early afterglow lightcurves. We find that $\lesssim16\%$ of short GRBs in our sample took place at densities $\lesssim10^{-4}$ cm$^{-3}$. These densities represent the expected range of values at distances greater than the host galaxy's virial radii. We find that out of the five SGRBs in our sample that have been found to be observationally hostless, none are consistent with having occurred beyond the virial radius of their birth galaxies. This implies one of two scenarios. Either these observationally hostless SGRBs occurred outside of the half-light radius of their host galaxy, but well within the galactic halo, or in host galaxies at moderate to high redshifts ($z\gtrsim 2$) that were missed by follow-up observations.
