Markarian 6 Nucleus since 1992

Abstract

We present results of an optical spectral monitoring campaign of the Seyfert galaxy Markarian 6 for a period of nearly 6 years between 1992 January and 1997 November carried out with a CCD spectrograph at the 2.6 m Shajn Telescope of the Crimean Astrophysical Observatory. Our data set consists of 104 Hβ region spectra and 56 Hα region spectra. Light curves for Hα and Hβ emission lines, and the continuum at two bands near these lines, are given. The continuum variations are generally smooth and very pronounced. The Hβ emission line is found to respond to continuum variations with a time lag of 18±2 days. The Hα line has a similar lag. The continuum variations at 5170 and 7030 A are tightly correlated, pointing to no evidence for changes in the nonstellar continuum color in optics. A lag of about 5 days between these two continuum bands is suspected. The blue wing lags behind the red wing, ruling out a radial outflow in the broad-line region (BLR) and, in particular, the biconical outflow as responsible for the bumps in the broad-line profiles. We find that some changes in the profile shapes of Balmer emission lines in Mrk 6 are related to neither the matter redistribution nor the reverberation effects, but probably are driven by the changes in the anisotropy of the ionizing radiation. The Hβ emission-line profile at Vr = ±3000 km s-1 and the optical continuum show a well-correlated variability (with a lag), while the poor correlation for the profile segment at Vr = +1300 km s-1 can indicate the presence of two components in the broad-line profiles. One of the components has a double-peaked structure and is associated with the well-known blue bump observed in the Balmer profiles in Mrk 6.