Deep Chandra study of the truncated cool core of the Ophiuchus cluster
  We present the results of a deep (280 ks) Chandra observation of the
Ophiuchus cluster, the second-brightest galaxy cluster in the X-ray sky. The
cluster hosts a truncated cool core, with a temperature increasing from kT~1
keV in the core to kT~9 keV at r~30 kpc. Beyond r~30 kpc the intra-cluster
medium (ICM) appears remarkably isothermal. The core is dynamically disturbed
with multiple sloshing induced cold fronts, with indications for both
Rayleigh-Taylor and Kelvin-Helmholtz instabilities. The sloshing is the result
of the strongly perturbed gravitational potential in the cluster core, with the
central brightest cluster galaxy (BCG) being displaced southward from the
global center of mass. The residual image reveals a likely subcluster south of
the core at the projected distance of r~280 kpc. The cluster also harbors a
likely radio phoenix, a source revived by adiabatic compression by gas motions
in the ICM. Even though the Ophiuchus cluster is strongly dynamically active,
the amplitude of density fluctuations outside of the cooling core is low,
indicating velocities smaller than ~100 km/s. The density fluctuations might be
damped by thermal conduction in the hot and remarkably isothermal ICM,
resulting in our underestimate of gas velocities. We find a surprising, sharp
surface brightness discontinuity, that is curved away from the core, at r~120
kpc to the southeast of the cluster center. We conclude that this feature is
most likely due to gas dynamics associated with a merger and not a result of an
extraordinary active galactic nucleus (AGN) outburst. The cooling core lacks
any observable X-ray cavities and the AGN only displays weak, point-like radio
emission, lacking lobes or jets, indicating that currently it may be largely
dormant. The lack of strong AGN activity may be due to the bulk of the cooling
taking place offset from the central supermassive black hole.
