A LOW-MASS BLACK HOLE IN THE NEARBY SEYFERT GALAXY UGC 06728

We present the results of a recent reverberation mapping campaign for UGC 06728, a nearby low-luminosity Seyfert 1 in a late-type galaxy. Nightly monitoring in the spring of 2015 allowed us to determine an H beta time delay of tau= 1.4. +/- 0.8 days. Combined with the width of the variable H beta line profile, we determine a black hole mass of M-BH= 7.1. +/- 4.0 )x 10(5) M circle dot We also constrain the bulge stellar velocity dispersion from higher-resolution longslit spectroscopy along the galaxy minor axis and find s. = 51.6 +/- 4.9 km s(-1). The measurements presented here are in good agreement with both the RBLR-L relationship and the MBH-s. relationship for active galactic nuclei. Combined with a previously published spin measurement, our mass determination for UGC 06728 makes it the lowest-mass black hole that has been fully characterized, and thus an important object to help anchor the low-mass end of black hole evolutionary models.