Chandra Observations of Abell 2261 Brightest Cluster Galaxy, a Candidate
  Host to a Recoiling Black Hole
  We use Chandra X-ray observations to look for evidence of a recoiling black
hole from the brightest cluster galaxy in Abell 2261 (A2261-BCG). A2261-BCG is
a strong candidate for a recoiling black hole because of its large, flat
stellar core, revealed by Hubble Space Telescope imaging observations. We took
100-ksec observations with Chandra and combined it with 35 ksec of archival
observations to look for low-level accretion onto a black hole of expected mass
$M\sim10^{10}\ M_{\scriptscriptstyle \odot}$ that could possibly be located in
one of four off-center stellar knots near the galaxy's center or else in the
optical center of the galaxy or in the location of radio emission. We found no
X-ray emission arising from a point source in excess of the cluster gas and can
place limits on the accretion of any black hole in the central region to a 2-7
keV flux below $4.3 \times 10^{-16}\ \mathrm{erg\ s^{-1}\ cm^{-2}}$,
corresponding to a bolometric Eddington fraction of about $10^{-6}$. Thus there
is either no $10^{10}\ M_{\scriptscriptstyle \odot}$ black hole in the core of
A2261-BCG, or it is accreting at a low level. We also discuss the morphology of
the X-ray emitting gas in the cluster and how its asymmetry is consistent with
a large dynamic event.
