Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. III. Optical Variability and X‐Ray/UV/Optical Correlations

We present optical observations of the low-luminosity Seyfert 1 nucleus ofNGC 4395, as part of a multiwavelength reverberation-mapping program.Observations were carried out over two nights in 2004 April at Lick, Wise, andKitt Peak Observatories. We obtained V-band and B-band photometry, and spectraover the range 3500-6800 Angstroms. Simultaneous Hubble Space Telescope UV andChandra X-ray observations are presented in companion papers. Even though NGC4395 was in an extremely low state of activity, we detect significant continuumvariability of 2-10%, increasing toward shorter wavelengths. The continuumlight curves, both spectroscopic and photometric, are qualitatively similar tothe simultaneous UV and X-ray light curves. Inter-band cross-correlationssuggest that the optical continuum emission lags behind the UV continuumemission by 24 +7/-9 min, and that the optical continuum emission lags behindthe X-ray continuum emission by 44 +/- 13 min, consistent with a reprocessingmodel for active galactic nucleus emission. There are also hints of Balmeremission lines lagging behind the optical continuum by an amount slightlylarger than the emission-line lag detected in the UV. These results are allsimilar to those of other Seyfert 1 nuclei. The emission-line lag yields a massmeasurement of the central black hole, which although not very significant, isconsistent with the value derived from the simultaneous UV data.Comment: 29 pages, 16 figures, emulateapj, accepted for publication in Ap