Spectral optical monitoring of a double-peaked emission line AGN Arp 102B: Variability of spectral lines and continuum

Abstract

Context. We present results of long-term (1987-2010) optical spectral monitoring of the broad-line radio galaxy Arp 102B, a prototype of an active galactic nucleus with double-peaked broad emission lines that are commonly assumed to be emitted from an accretion disk. Aims. To explore the structure of the broad-line region (BLR), we analyze the light-curves of the broad Hα and Hβ lines and the continuum flux. We aim to estimate the dimensions of the broad-line emitting regions and the mass of the central black hole. Methods. We used the cross correlation function to find lags between the lines and continuum variations. We investigated the correlation between line and continuum fluxes in more detail and explored periodical variations of the red-to-blue line flux ratio using Lomb-Scargle periodograms. Results. The line and continuum light-curves show several flare-like events. The fluxes in lines and in the continuum show no significant change (around 20%) during the monitored period. We found a weak correlation between the line and continuum flux variation that may indicate that the line variation is weakly connected with the variation of the central photoionization source. In spite of this weak line-continuum correlation, we estimated a time lag for Hβ of about 20 days using various methods. The correlation between the Hβ and Hα flux variation is significantly higher than that between the lines and continuum. During the monitored period, the Hβ and Hα lines show double-peaked profiles, and we found an indication for a periodical oscillation in the red-to-blue flux ratio of the Hα line. The estimated mass of the central black hole is ~1.1 × 108 M, which agrees with the mass estimated from the M-σ *-relation. © 2013 ESO.