A High Resolution View of the Warm Absorber in the Quasar MR2251-178
  High resolution X-ray spectroscopy of the warm absorber in the nearby quasar,
MR2251-178 (z = 0.06398) is presented. The observations were carried out in
2011 using the Chandra High Energy Transmission Grating and the XMM-Newton
Reflection Grating Spectrometer, with net exposure times of approximately 400
ks each. A multitude of absorption lines from C to Fe are detected, revealing
at least 3 warm absorbing components ranging in ionization parameter from
log(\xi/erg cm s^-1) = 1-3 and with outflow velocities < 500 km/s. The lowest
ionization absorber appears to vary between the Chandra and XMM-Newton
observations, which implies a radial distance of between 9-17 pc from the black
hole. Several broad soft X-ray emission lines are strongly detected, most
notably from He-like Oxygen, with FWHM velocity widths of up to 10000 km/s,
consistent with an origin from Broad Line Region (BLR) clouds. In addition to
the warm absorber, gas partially covering the line of sight to the quasar
appears to be present, of typical column density N_H = 10^23 cm^-2. We suggest
that the partial covering absorber may arise from the same BLR clouds
responsible for the broad soft X-ray emission lines. Finally the presence of a
highly ionised outflow in the iron K band from both 2002 and 2011 Chandra HETG
observations appears to be confirmed, which has an outflow velocity of -15600
\pm 2400 km/s. However a partial covering origin for the iron K absorption
cannot be excluded, resulting from low ionization material with little or no
outflow velocity.
