Probing within the Bondi radius of the ultramassive black hole in NGC
  1600
  We present deep (250 ks) Chandra observations of the nearby galaxy group NGC
1600, which has at its centre an ultramassive black hole (17$\pm$1.5 billion
M$_{\odot}$). The exceptionally large mass of the black hole coupled with its
low redshift makes it one of only a handful of black holes for which spatially
resolved temperature and density profiles can be obtained within the Bondi
radius with the high spatial resolution of Chandra. We analyzed the hot gas
properties within the Bondi accretion radius R$_B$=1.2" - 1.7"= 0.38 - 0.54
kpc. Within a $\sim\!3$ kpc radius, we find two temperature components with
statistical significance. Both the single temperature and two temperature
models show only a very slight rise in temperature towards the centre, and are
consistent with being flat. This is in contrast with the expectation from Bondi
accretion for a temperature profile which increases towards the centre, and
appears to indicate that the dynamics of the gas are not being determined by
the central black hole. The density profile follows a relatively shallow
$\rho\propto~r^{-[0.61\pm0.13]}$ relationship within the Bondi radius, which
suggests that the true accretion rate on to the black hole may be lower than
the classical Bondi accretion rate.
