Fast Extragalactic X-ray Transients From Binary Neutron Star Mergers

The observed light curves and other properties of the two extragalactic fast x-ray transients, CDF-S XT1 and CDF-S XT2, which were discovered recently in archival data of the Chandra Deep Field-South (CDF-S) observations, indicate that they belong to two different populations of x-ray transients. XT1 seems to be an x-ray flash, i.e., a narrowly beamed long duration gamma ray burst viewed from far off axis, while XT2 seems to be a nebular emission powered by a newly born millisecond pulsar in a binary neutron stars merger.