Short and long time-scales variability of the H α double-peaked profile of Pictor A

Abstract

ABSTRACT We present the results of the analysis of 18 optical spectra covering the H α profile region of the active nucleus of the galaxy Pictor A obtained in different epochs along 12 yr. With these data, we model the variability of the double-peaked H α emission of the nucleus of this galaxy. We find small variations in the integrated flux of the broad component of H α, occurring on short time-scales, of the order of 40 d. In addition, significant variations in the relative intensities of the red and blue sides of the broad profile occur on time-scales of years. In order to explain the observations, we propose a scenario in which the double-peak profile is produced by a flattened distribution of clouds surrounding the accretion disc with Keplerian and relativistic orbits, inclined in relation to the sky plane, and with axially asymmetric surface emissivity with the radius of maximum emissivity. We find that, for the theoretical time-scales of the disc-like BLR to conform the time-scales of variation observed for the double-peak profile, it is necessary for the gas in the disc to orbit a SMBH with a mass of M• $\approx \, 2\times$ $10^{8}\, \mbox{M}_\odot$. In this scenario, the physical extension of the line-emitting region extends by 6–48 light-days from the SMBH.