An X-ray variable absorber within the Broad Line Region in Fairall 51

TL;DR

This study analyzes the X-ray spectral variability of Fairall 51, revealing an absorber within the Broad Line Region that influences the galaxy's X-ray properties and is linked to the accretion processes near the black hole.

Contribution

It provides the first detailed timing and spectral analysis of Fairall 51's X-ray absorption, identifying a variable absorber in the Broad Line Region and measuring the black hole's spin.

Findings

Variable ionized absorber affects X-ray spectra.

Absorber located approximately 0.05 pc from the center.

Black hole spin estimated at ~0.8.

Abstract

Fairall 51 is a polar-scattered Seyfert 1 galaxy, a type of active galaxies believed to represent a bridge between unobscured type-1 and obscured type-2 objects. Fairall 51 has shown complex and variable X-ray absorption but only little is known about its origin. In our research, we observed Fairall 51 with the X-ray satellite Suzaku in order to constrain a characteristic time-scale of its variability. We performed timing and spectral analysis of four observations separated by 1.5, 2 and 5.5 day intervals. We found that the 0.5-50 keV broadband X-ray spectra are dominated by a primary power-law emission (with the photon index ~ 2). This emission is affected by at least three absorbers with different ionisations (log(xi) ~ 1-4). The spectrum is further shaped by a reprocessed emission, possibly coming from two regions -- the accretion disc and a more distant scattering region. The accretion disc emission is smeared by the relativistic effects, from which we measured the spin of the black hole as a ~ 0.8 (+-0.2). We found that most of the spectral variability can be attributed to the least ionised absorber whose column density changed by a factor of two between the first (highest-flux) and the last (lowest-flux) observation. A week-long scale of the variability indicates that the absorber is located at the distance ~ 0.05 pc from the centre, i.e., in the Broad Line Region.