An Ultraluminous Supersoft Source in a Dwarf Galaxy of Abell 85: An
  Intermediate-Mass Black Hole Candidate
  We study a large sample of dwarf galaxies using archival Chandra X-ray
observations, with the aim of detecting accreting intermediate-mass black holes
(IMBHs). IMBHs are expected to inhabit dwarf galaxies and to produce specific
signatures in terms of luminosity and X-ray spectra. We report the discovery of
an X-ray source associated with an Abell 85 dwarf galaxy that fits the IMBH
description. The stellar mass of the host galaxy is estimated to be 2 $\times$
10$^8$ $M_\odot$, which makes it one of the least massive galaxies to
potentially host an accreting black hole. The source is detected in the soft
band, under 1 keV, while undetected at higher energies. The X-ray luminosity is
$\approx$ 10$^{41}$ erg s$^{-1}$, making it almost three orders of magnitude
more luminous than the most luminous stellar-mass supersoft emitters. From the
galaxy stellar mass vs. black hole mass relation, we estimate the mass to be
within the intermediate regime. Another method that resulted in an intermediate
mass relies on the fact that supersoft emission is expected to be associated
with high accretion rates, approaching the Eddington limit. We suggest that the
observed offset of the X-ray source from the galactic center ($\approx$ 1.8
kpc) is due to galaxy interactions, and we present evidence from the literature
that supports the relation between black hole activity and galaxy interactions.
