Multiwavelength Follow-up Observations of the Tidal Disruption Event
  Candidate 2XMMi J184725.1-631724
  The ultrasoft X-ray flare 2XMMi J184725.1-631724 was serendipitously detected
in two XMM-Newton observations in 2006 and 2007, with a peak luminosity of
6X10^43 erg/s. It was suggested to be a tidal disruption event (TDE) because
its position is consistent with the center of an inactive galaxy. It is the
only known X-ray TDE candidate whose X-ray spectra showed evidence of a weak
steep powerlaw component besides a dominant supersoft thermal disk. We have
carried out multiwavelength follow-up observations of the event. Multiple X-ray
monitorings show that the X-ray luminosity has decayed significantly after
2011. Especially, in our deep Chandra observation in 2013, we detected a very
faint counterpart that supports the nuclear origin of 2XMMi J184725.1-631724
but had an X-ray flux a factor of ~1000 lower than in the peak of the event.
Compared with follow-up UV observations, we found that there might be some
enhanced UV emission associated with the TDE in the first XMM-Newton
observation. We also obtained a high-quality UV-optical spectrum with the SOAR
and put a very tight constraint on the persistent nuclear activity, with a
persistent X-ray luminosity expected to be lower than the peak of the flare by
a factor of >2700. Therefore, our multiwavelength follow-up observations
strongly support the TDE explanation of the event.
