Long-term optical spectral monitoring of NGC 7469

Abstract

We present the results of the long-term (20-year period, from 1996 to 2015) optical spectral monitoring of the Seyfert 1 galaxy NGC 7469. The variation in the light curves of the broad He II λ4686 Å Hβ and Hα lines, and the continuum at 5100 and 6300 Å have been explored. The maximum activity was in 1998, and the variability in the continuum and lines seems to have two periods of around 1200 and 2600 d; however, these periodicities should be taken with caution because of the red noise. Beside these periods, there are several short-term (1-5 d) flare-like events in the light curves. There are good correlations between the continuum fluxes and Hα and Hβ line fluxes, but significantly smaller correlation between the He II and continuum. We found that the time-lags between the continuum and broad lines are different for Hβ [∼20 light day (l.d.)] and Hα (∼3 l.d.), and that He II also has a smaller lag (∼2-3 l.d.). The Hα and Hβ line profiles show a slight red asymmetry, and the broad-line profiles did not change in the 20-year period. Using the lags and widths of Hα and Hβ, we estimated the central black hole mass and found that it is ∼(1-6) × 107 M☉, which is in agreement with previous reverberation estimates.