Variable X-ray absorption in the mini-BAL QSO PG 1126-041^⋆

¹ Dipartimento di Astronomia, Università degli Studi di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: giustini@iasfbo.inaf.it
² INAF - Istituto di Astrofisica Spaziale e Fisica cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
³ Department of Astronomy and Astrophysics, the Pennsylvania State University, 525 Davey Lab, University Park, PA 166802, USA
⁴ Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424, USA
⁵ Center for Gravitational Wave Physics, the Pennsylvania State University, University Park, PA 166802, USA
⁶ School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
⁷ Department of Physics and Astronomy, University of Nevada Las Vegas, 4505 Maryland Pkwy Las Vegas, NV 891541-4002, USA
⁸ X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁹ Department of Astronomy and CRESST, University of Maryland, College Park, MD 20742, USA
¹⁰ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy

Received: 19 July 2011
Accepted: 27 September 2011

Abstract

Context. 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.

Aims. 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.

Methods. 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.

Results. 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 (υ_X ~ 16   500 km s^-1) than the UV absorbing one (υ_uv ~ 5000 km s^-1). This highly ionized absorber is found to be variable on very short (a few kiloseconds) time scales.

Conclusions. 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.