  The Seyfert 1 galaxy Zw 229-015 is among the brightest active galaxies being
monitored by the Kepler mission. In order to determine the black hole mass in
Zw 229-015 from H-beta reverberation mapping, we have carried out nightly
observations with the Kast Spectrograph at the Lick 3m telescope during the
dark runs from June through December 2010, obtaining 54 spectroscopic
observations in total. We have also obtained nightly V-band imaging with the
Katzman Automatic Imaging Telescope at Lick Observatory and with the 0.9m
telescope at the Brigham Young University West Mountain Observatory over the
same period. We detect strong variability in the source, which exhibited more
than a factor of 2 change in broad H-beta flux. From cross-correlation
measurements, we find that the H-beta light curve has a rest-frame lag of
3.86(+0.69,-0.90) days with respect to the V-band continuum variations. We also
measure reverberation lags for H-alpha and H-gamma and find an upper limit to
the H-delta lag. Combining the H-beta lag measurement with a broad H-beta width
of sigma = 1590+/-47 km/s measured from the root-mean-square variability
spectrum, we obtain a virial estimate of M_BH = 1.00(-0.24,+0.19)*10^7 solar
masses for the black hole in Zw 229-015. As a Kepler target, Zw 229-015 will
eventually have one of the highest-quality optical light curves ever measured
for any active galaxy, and the black hole mass determined from reverberation
mapping will serve as a benchmark for testing relationships between black hole
mass and continuum variability characteristics in active galactic nuclei.
