The Lick AGN Monitoring Project 2011: Reverberation Mapping of Markarian 50

The Lick AGN Monitoring Project 2011 observing campaign was carried out over the course of 11 weeks in spring 2011. Here we present the first results from this program, a measurement of the broad-line reverberation lag in the Seyfert 1 galaxy Mrk 50. Combining our data with supplemental observations obtained prior to the start of the main observing campaign, our data set covers a total duration of 4.5 months. During this time, Mrk 50 was highly variable, exhibiting a maximum variability amplitude of a factor of similar to 4 in the U-band continuum and a factor of similar to 2 in the H beta line. Using standard cross-correlation techniques, we find that H beta and H gamma lag the V-band continuum by tau(cen) = 10.64(-0.93)(+0.82) and 8.43(-1.28)(+1.30) days, respectively, while the lag of He II lambda 4686 is unresolved. The H beta line exhibits a symmetric velocity-resolved reverberation signature with shorter lags in the high-velocity wings than in the line core, consistent with an origin in a broad-line region (BLR) dominated by orbital motion rather than infall or outflow. Assuming a virial normalization factor of f = 5.25, the virial estimate of the black hole mass is (3.2 +/- 0.5) x 10(7) M-circle dot. These observations demonstrate that Mrk 50 is among the most promising nearby active galaxies for detailed investigations of BLR structure and dynamics.