Extragalactic fast X-ray transient candidates discovered by Chandra (2000–2014)

Vol. 663
4. Extragalactic astronomy

Extragalactic fast X-ray transient candidates discovered by Chandra (2000–2014)

by J. Quirola-Vasquez, F.E. Bauer, P.G. Jonker, et al. 2022, A&A, 663, A168

Thanks to the continuously improving sensitivity of X-ray instruments, unexplained short X-ray flares, lasting from a few seconds to hours, have recently been discovered. These fast extragalactic X-ray transients (FEXTs) are a particularly understudied population. Two events were discovered in nearby galaxies with an underlying quiescent emission. Another two were discovered in the Chandra Deep Field South data, and a fifth FEXT was discovered during a Chandra calibration observation of the cluster Abell 1795. Quirola-Vasquez and collaborators carried out one of the first systematic searches for FXRTs in the Chandra Source Catalog. They detected 14 FXRT candidates. The nature of FEXTs remains a mystery. The increased sample allows the authors to derive the event rate. This rate is consistent with the volumetric rate of long and short gamma-ray bursts and tidal disruption events, but well below the rate of supernovae. This shows the rarity of this type of event.