Markarian 6: shocking the environment of an intermediate Seyfert
  Markarian 6 is a nearby (D~78 Mpc) Seyfert 1.5, early-type galaxy, with a
double set of radio bubbles. The outer set spans ~7.5 kpc and is expanding into
the halo regions of the host galaxy. We present an analysis of our new Chandra
observation, together with archival XMM-Newton data, to look for evidence of
emission from shocked gas around the external radio bubbles, both from
spatially resolved regions in Chandra and from spectral analysis of the XMM
data. We also look for evidence of a variable absorbing column along our line
of sight to Mrk 6, to explain the evident differences seen in the AGN spectra
from the various, non-contemporaneous, observations.
  We find that the variable absorption hypothesis explains the differences
between the Chandra and XMM spectra, with the Chandra spectrum being heavily
absorbed. The intrinsic N_H varies from ~8x10^{21} atoms*cm^{-2} to ~3x10^{23}
atoms*cm^{-2} on short timescales (2-6 years). The past evolution of the source
suggests this is probably caused by a clump of gas close to the central AGN,
passing in front of us at the moment of the observation. Shells of thermal
X-ray emission are detected around the radio bubbles, with a temperature of
~0.9 keV. We estimate a temperature of ~0.2 keV for the external medium using
luminosity constraints from our Chandra image. We analyse these results using
the Rankine-Hugoniot shock jump conditions, and obtain a Mach number of ~3.9,
compatible with a scenario in which the gas in the shells is inducing a strong
shock in the surrounding ISM. This could be the third clear detection of strong
shocks produced by a radio-powerful Seyfert galaxy. These results are
compatible with previous findings on Centaurus A and NGC 3801, supporting a
picture in which these AGN-driven outflows play an important role in the
environment and evolution of the host galaxy.
