Line profile and continuum variability in the very broad-line Seyfert galaxy Mrk 926^*

Institut für Astrophysik, Universität Göttingen, Friedrich-Hund Platz 1, 37077 Göttingen, Germany
e-mail: wkollat@astro.physik.uni-goettingen.de

Received: 13 October 2009
Accepted: 8 June 2010

Abstract

Aims. We present results of an intensive spectroscopic variability campaign of the very broad-line Seyfert 1 galaxy Mrk 926. Our aim is to investigate the broad-line region (BLR) by studying the intensity and line profile variations of this galaxy on short timescales.

Methods. High signal-to-noise ratio (S/N) spectra were taken with the 9.2 m Hobby-Eberly Telescope (HET) in identical conditions during two observing campaigns in 2004 and 2005. After the spectral reduction and internal calibration we achieved a relative flux accuracy of better than 1%.

Results. The rms profiles of the very broad Balmer lines have shapes that differ from their mean line profiles, consisting of two inner (v ≲  ± 6000 km s^-1) and two outer (v ≳  ± 6000 km s^-1) line components in addition to a central component (v ≲  ± 600 km s^-1). These outer and inner line segments varied with different amplitudes during our campaign. The radius of the BLR is very small with an upper limit of 2 light-days for the Hβ BLR size. We derived an upper limit to the central black hole mass of M = 11.2 × 10⁷M_⊙. The 2-D cross-correlation functions CCF(τ, v) of Hβ and Hα are flat within the error limits. The response of the Balmer line segments with respect to continuum variations is different in the outer and inner wings of Hα and Hβ. This double structure in the response curves – of two separate inner and outer components – has also been seen in the rms line profiles. We conclude that the outer and inner line segments originate in different regions and/or under different physical conditions.