Abstract:
The X-ray source 2XMM J123103.2+110648 was previously found to show pure thermal
X-ray spectra and an ∼3.8 h periodicity in three XMM–Newton X-ray observations in 2003–
2005, and the optical spectrum of the host galaxy suggested it as a type 2 active galactic nucleus
candidate. We have obtained new X-ray observations of the source, with Swift and Chandra in
2013–2016, in order to shed new light on its nature based on its long-term evolution property.
We found that the source could be in an X-ray outburst, with the X-ray flux decreasing by an
order of magnitude in the Swift and Chandra observations, compared with the XMM–Newton
observations 10 yr ago. There seemed to be significant spectral softening associated with the
drop of X-ray flux (disc temperature kT ∼ 0.16–0.2 keV in XMM–Newton observations versus
kT ∼ 0.09 ± 0.02 keV in the Chandra observation). Therefore, the Swift and Chandra followup
observations support our previous suggestion that the source could be a tidal disruption
event (TDE), though it seems to evolve slower than most of the other TDE candidates. The
apparent long duration of this event could be due to the presence of a long super-Eddington
accretion phase and/or slow circularization.
