  Mrk926 is known to be a highly variable AGN with very broad line profiles. We
studied the continuum and line profile variations of this object with high
temporal resolution in order to determine its broad-line region structure and
to derive its 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 at the Wise Observatory, over a period of about five months. We extracted
spectroscopic continuum and line light curves, and computed CCFs as well as
velocity-resolved CCFs with respect to the combined continuum V-band light
curve. The continuum luminosity of Mrk926 showed a drastic decrease during our
campaign: it dropped to less than 50% of its original value within only 2.5
months. The spectra show complex and very broad Balmer line profiles, including
outer Balmer satellites ranging from +-5000 to +-13,000 kms-1. The Ha, Hb, and
HeI5876 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 +- 5000 kms-1), at ~10 and ~57 ld and at ~5 and ~48
ld, respectively. These structures might be interpreted as the signature of a
line-emitting ring, inclined by ~50 deg to the line of sight and orbiting the
BH at radii, R, of 33.5 and 26.5 ld. We determined continuum luminosities,
log(lambda\,L_(lambda)/erg s-1), of 43.68 to 44.13, which are in good agreement
with the established R_(BLR)-L_(AGN) relation. We derive a black hole mass of
1.1 +- 0.2 * 10^8 M_solar; this indicates a low Eddington ratio, which
decreased from 8 to 3 percent during our campaign. The Balmer satellite
components show a response to the continuum variations on 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.
