A new X-ray tidal disruption event candidate with fast variability
  During a close encounter between a star and a supermassive black hole, the
star can get disrupted by the black hole's tidal forces, resulting in a tidal
disruption event (TDE). The accretion of the star's material onto the black
hole produces strong emission in different wavelength regimes. Here we report
the discovery with ROSAT of an X-ray-selected transient source in an optically
non-active galaxy. At the location RA: 13h31m57.66s and Dec:
-32deg3arcmin19.7arsec a sudden rise in X-ray luminosity by a factor of 8
within 8 days has been observed. Additionally, a very soft X-ray spectrum with
a black-body temperature kT=0.1 keV and a peak luminosity of at least 10^43
erg/s suggest a TDE interpretation, and the observed properties are very
similar to previously identified soft X-ray (ROSAT) TDEs. An optical spectrum
taken of the galaxy at the position of RXJ133157.6-324319.7 six years after the
X-ray outburst does not show any emission lines as would be expected from a
persistent active galactic nucleus (AGN). The redshift of the galaxy is
determined to be 0.051 based on absorption lines. It is therefore likely a
member of the galaxy cluster Abell 3560. The rise in X-ray luminosity happens
within 8 days and thus appears to be fast for such an event. No X-ray emission
was detected 170 days before and 165 days after the event, and none was
detected 25 years later with the Neil Gehrels Swift Observatory. The change in
X-ray luminosity is at least a factor of 40.
