The Unusually High Halo Concentration of the Fossil Group NGC 6482:
  Evidence for Weak Adiabatic Contraction
  We revisit the massive isolated elliptical galaxy / fossil group NGC 6482 for
which previous X-ray studies of a modest Chandra observation obtained a very
uncertain, but also possibly very high, halo concentration. We present new
measurements of the hot gas surface brightness, temperature, and iron abundance
using the modest Chandra observation and a previously unpublished Suzaku
observation, the latter of which allows measurements of the gas properties to
be extended out to ~r_2500. By constructing hydrostatic equilibrium models of
the gas with separate components for the gas, BCG stellar mass, and the dark
matter (DM), we measure c_200 = 32.2 +/- 7.1 and M_200 = (4.5 +/- 0.6 x 10^12
M_sun using an NFW DM profile. For a halo of this mass, c_200 exceeds the mean
value (7.1) expected for relaxed LCDM halos by $3.5 \sigma$ in terms of the
observational error, and by $6 \sigma$ considering the intrinsic scatter in the
LCDM c-M relation, which situates NGC 6482 as the most extreme outlier known
for a fossil system. We explored several variants of adiabatic contraction (AC)
models and, while the AC models provide fits of the same quality as the
un-contracted models, they do have the following advantages: (1) smaller c_200
that is less of an outlier in the LCDM c-M relation, and (2) baryon fractions
that agree better with the mean cosmic value. While the standard AC
prescriptions yield a BCG stellar mass that is uncomfortably small compared to
results from stellar population synthesis (SPS) models, a weaker AC variant
that artificially shuts off cooling and star formation at z=2 yields the same
stellar mass as the un-contracted models. For these reasons, we believe our
X-ray analysis prefers this weaker AC variant applied to either an NFW or
Einasto DM halo. Finally, the BCG stellar mass strongly favors SPS models with
a Chabrier or Kroupa IMF over a Salpeter IMF. (Abridged)
