Spectral optical monitoring of a double-peaked emission line AGN Arp
  102B: I. Variability of spectral lines and continuum
  Here we present results of the long-term (1987-2010) optical spectral
monitoring of the broad line radio galaxy Arp 102B, a prototype of active
galactic nuclei with the double-peaked broad emission lines, usually assumed to
be emitted from an accretion disk.
  To explore the structure of the broad line region (BLR), we analyze the light
curves of the broad H\alpha and H\beta 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.
  We use the CCF to find lags between the lines and continuum variations. We
investigate in more details the correlation between line and continuum fluxes,
moreover we explore periodical variations of the red-to-blue line flux ratio
using Lomb-Scargle periodograms.
  The line and continuum light curves show several flare-like events. The
fluxes in lines and in the continuum are not showing a big change (around 20%)
during the monitoring period. We found a small correlation between the line and
continuum flux variation, that may indicate that variation in lines has weak
connection with the variation of the central photoionization source. In spite
of a low line-continuum correlation, using several methods, we estimated a time
lag for H\beta around 20 days. The correlation between the H\beta and H\alpha
flux variation is significantly higher than between lines and continuum. During
the monitoring period, the H\beta and H\alpha lines show double-peaked profiles
and we found an indication for a periodical oscillation in the red-to-blue flux
ratio of the H\alpha line. The estimated mass of the central black hole is \sim
1.1 \times 10^8 M\odot that is in an agreement with the mass estimated from the
M-\sigma* relation.
