Reverberation Mapping Of The Kepler Field AGN Ka1858+4850

KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among the brightest active galaxies monitored by the Kepler mission. We have carried out a reverberation mapping campaign designed to measure the broad-line region size and estimate the mass of the black hole in this galaxy. We obtained 74 epochs of spectroscopic data using the Kast Spectrograph at the Lick 3 m telescope from 2012 February to November, and obtained complementary V-band images from five other ground-based telescopes. We measured the H beta light curve lag with respect to the V-band continuum light curve using both cross-correlation techniques (CCF) and continuum light curve variability modeling with the JAVELIN method and found rest-frame lags of tau(CCF) = 13.53(+2.03)(-2.32) days and tau(JAVELIN) = 13.15(+1.08)(-1.00) days. The H beta rms line profile has a width of sigma line = 770 +/- 49 km s(-1). Combining these two results and assuming a virial scale factor of f = 5.13, we obtained a virial estimate of M-BH = 8.06(+1.59)(-1.72) x 10(6) M circle dot for the mass of the central black hole and an Eddington ratio of L/L-Edd approximate to 0.2. We also obtained consistent but slightly shorter emission-line lags with respect to the Kepler light curve. Thanks to the Kepler mission, the light curve of KA1858+4850 has among the highest cadences and signal-to-noise ratios ever measured for an active galactic nucleus; thus, our black hole mass measurement will serve as a reference point for relations between black hole mass and continuum variability characteristics in active galactic nuclei.