The Mass of the Black Hole in the Seyfert 1 Galaxy NGC 4593 from   Reverberation Mapping
  We present new observations leading to an improved black hole mass estimate for the Seyfert 1 galaxy NGC 4593 as part of a reverberation-mapping campaign conducted at the MDM Observatory. Cross-correlation analysis of the H_beta emission-line light curve with the optical continuum light curve reveals an emission-line time delay of 3.73 (+-0.75) days. By combining this time delay with the H_beta line width, we derive a central black hole mass of M_BH = 9.8(+-2.1)x10^6 M_sun, an improvement in precision of a factor of several over past results. 
Kelly D. Denney (1), Misty C. Bentz (1), Bradley M. Peterson (1),   Richard W. Pogge (1), Edward M. Cackett (2), Matthias Di...