Long-term optical spectral monitoring of NGC 7469

TL;DR

This 20-year optical spectral study of NGC 7469 reveals variability patterns, line-lag differences, and estimates the black hole mass, contributing long-term observational data to Seyfert galaxy research.

Contribution

It provides the first long-term (20-year) spectral monitoring data of NGC 7469, analyzing variability, line correlations, and black hole mass estimation.

Findings

Detected two main variability periods (~1200 and 2600 days) with caution due to red-noise.

Found different time-lags for Hα (~3 days), Hβ (~20 days), and He II (~2-3 days).

Estimated black hole mass as (1-6)×10^7 solar masses, consistent with previous reverberation results.

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 {\lambda}4686A H{\beta} and H{\alpha} lines, and the continuum at 5100A and 6300A have been explored. The maximum of activity was in 1998, and the variability in the continuum and lines seems to have two periods of around 1200 and 2600 days, however these periodicities should be taken with caution because of the red-noise. Beside these periods, there are several short-term (1-5 days) flare-like events in the light-curves. There are good correlations between the continuum fluxes and H{\alpha} and H{\beta} 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 H{\beta} (~20 l.d.) and H{\alpha} (~3 l.d.), and that He II also has a smaller lag (~2-3 l.d.). The H{\alpha} and H{\beta} line profiles show a slight red asymmetry, and the broad line profiles did not changed in the 20-year period. Using the lags and widths of H{\alpha} and H{\beta} we estimated the central black hole mass and found that it is ~(1-6)x$10^7 M_{\odot}$, which is in agreement with previous reverberation estimates.