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Description
Mrk926 is known to be a highly-variable AGN. Furthermore, it is known to show very broad-line profiles. We intended to study the continuum and line profile variations of this object with high temporal resolution in order to determine its broad-line region (BLR) structure, and to derive its black hole (BH) mass. We carried out a high-cadence spectroscopic variability campaign of Mrk926 with the 10m HET telescope, aided by photometric V-band data taken with the C18 telescope at the Wise Observatory, over a period of about five months. We extracted spectroscopic continuum and line light curves, and computed cross-correlation functions (CCFs) as well as velocity-resolved CCFs with respect to the combined spectroscopic and photometric V-band light curve. The continuum luminosity of Mrk926 showed a drastic decrease during our campaign. The luminosity dropped to less than 50% of its original luminosity within 2.5 months only. Furthermore, the spectra of Mrk926 show complex and very broad Balmer line profiles including outer Balmer satellites ranging from +/-5000 to +/-13000km/s. The integrated H{alpha}, H{beta} and HeI_5876_ line light curves are delayed relative to the continuum light curve. The Ha and Hb lines show two velocity-delay structures in the central part of their line profile (within +/-5000km/s) at ~10 and ~57 light-days, and at ~5 and ~48 light-days, respectively. These structures might be interpreted as the upper and lower half of an ellipse in the velocity-delay plane, that might be the signature of a line-emitting ring, inclined by ~50{deg} to the line of sight, orbiting the black hole at radii R of 33.5 and 26.5 light-days. We determined continuum luminosities log({lambda}*L_({lambda})_/erg/s) of 43.68 to 44.13 which are in good agreement with the established R_(BLR)-L_(AGN) relation. Adopting delays of 33.5 and 26.5 days for Ha and Hb, respectively, we derive a black hole mass of 1.1+/-0.2*10^8^M_{sun}_ which indicates a low Eddington ratio decreasing from 8 to 3 percent during our campaign. The Balmer satellite components show a higher correlation coefficient with respect to the continuum than the central line profile, and their response to the continuum variations is of the order of only 3-5 days. We attribute this to the central line segment and the Balmer satellites having different, spatially distinct regions of origin.
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