Spectral activity of the Seyfert galaxy Markarian 6 in 1970–1991

¹ Crimean Laboratory of the Sternberg Astronomical Institute, University of Moscow, Russia; P/O Nauchny, 98409 Crimea, Ukraine Isaac Newton Institute of Chile, Crimean Branch
² Crimean Astrophysical Observatory, P/O Nauchny, 98409 Crimea, Ukraine Isaac Newton Institute of Chile, Crimean Branch e-mail: sergeev@crao.crimea.ua

Corresponding author: V. T. Doroshenko, doroshen@sai.crimea.ua

Received: 10 December 2002
Accepted: 21 March 2003

Abstract

We present results of the reduction of the archive spectra of the nucleus of Mrk 6 obtained in 1970–1991 using the image tube spectrograph at the 2.6-m Shajn telescope of the Crimean Astrophysical Observatory. We analyze 363 spectra for 181 dates obtained in the Hβ spectral region. The spectra in the Hα region (194 spectra for 179 dates) were used to get light curves. The light curves in the Hβ and Hα lines and also in the adjacent continuum show appreciable variability. Broad-line profile parameters (such as centroid, width, blue-to-red ratio of fluxes) seem to be independent of or dependent very weakly on the continuum flux. However, there is a tendency for the blue-to-red ratio of fluxes to increase with increasing continuum flux, and also a weak tendency for the profile width (profile dispersion) to decrease with increasing continuum flux. An anti-correlation between Hβ shapes at the blue and red wings, positive correlation between blue shape and line/continuum flux, and anti-correlation between red shape and line/continuum flux show that the blue segments respond slightly better to the continuum changes than the red segment and total Hβ line. We assume that the observed broad profile consists of at least two components with fixed profiles. We found that one of the components is nearly symmetric and has a single peak, while the other component has a blue bump and extended red wing. In terms of such a two-broad-components profile model, the evolution of the observed Hβ profiles can be roughly reproduced by changes in the relative strength of the two variable components. However, the evolution of the broad Hβ profile in Mrk 6 is complicated and not clear at all. The evolution is driven, most likely, by a set of various factor, including a multi-component BLR model with redistribution of ionizing radiation between different parts of the BLR, the matter redistribution, reverberation effects, and continuum-dependent changes.