Broadband photometric reverberation mapping of NGC4395

We present results of broadband photometric reverberation mapping (RM) to measure the radius of the broad-line region, and subsequently the black hole mass (M _BH), in the nearby, low-luminosity active galactic nuclei NGC4395. Using the Wise Observatory's 1m telescope equipped with the Sloan Digital Sky Survey g′, r′, and i′ broadband filters, we monitored NGC4395 for nine consecutive nights and obtained three light curves each with over 250 data points. The g′ and r′ bands include time variable contributions from Hβ and Hα, respectively, plus continuum. The i′ band is free of broad lines and covers exclusively continuum. We show that by looking for a peak in the difference between the cross-correlation and the auto-correlation functions for all combinations of filters, we can get a reliable estimate of the time lag necessary to compute M _BH. We measure the time lag for Hα to be 3.6 ± 0.8 hr, comparable to previous studies using the line-resolved spectroscopic RM method. We argue that this lag implies a black hole mass of M _BH = (4.9 ± 2.6) × 10⁴ M _⊙.