Variable X-ray absorption in the mini-BAL QSO PG 1126-041
  X-ray studies of active galactic nuclei (AGN) with powerful nuclear winds are
important for constraining the physics of the inner accretion/ejection flow
around supermassive black holes (SMBHs) and for understanding the impact of
such winds on the AGN environment. Our main scientific goal is to constrain the
properties of the circum-nuclear matter close to the SMBH in the mini-broad
absorption line quasar (mini-BAL QSO) PG 1126-041 using a multi-epoch
observational campaign with XMM-Newton. We performed temporally resolved X-ray
spectroscopy and simultaneous UV and X-ray photometry on the most complete set
of observations and on the deepest X-ray exposure of a mini-BAL QSO ever. We
found complex X-ray spectral variability on time scales of both months and
hours, which is best reproduced by means of variable massive ionized absorbers
along the line of sight. As a consequence, the observed optical-to-X-ray
spectral index is found to be variable with time. In the highest
signal-to-noise observation we detected highly ionized X-ray absorbing material
outflowing much faster (v ~ 16500 km/s) than the UV absorbing one (v ~ 5000
km/s). This highly ionized absorber is found to be variable on very short (a
few kiloseconds) time scales. Our findings are qualitatively consistent with
line-driven accretion disk winds scenarios. Our observations have opened the
time-resolved X-ray spectral analysis field for mini-BAL QSOs. Only with future
deep studies will we be able to map the dynamics of the inner flow and
understand the physics of AGN winds and their impact on the environment.
