Fast Extragalactic X-Ray Transients from Gamma-Ray Bursts Viewed Far Off-axis

The observed light curves and estimated sky rate of fast extragalactic X-ray transients (XRTs) discovered in archival Chandra data indicate that they belong to two distinct XRT populations. The first population of relatively short duration pulses, which typically last less than few minutes seems to be pulses of X-ray flashes, which are nearby long-duration gamma-ray bursts viewed from far off-axis. The second population of much longer pulses, which typically last hours, seems to be the early-time isotropic afterglows of short gamma-ray bursts that are beamed away from Earth, as was shown in a previous paper.