H α reverberation mapping from broad-band photometry of dwarf type 1 Seyfert galaxy NGC 4395

Abstract

ABSTRACT NGC 4395 is a dwarf type 1 Seyfert galaxy with a possible intermediate-mass black hole of several $\rm {10^4}$ solar masses in its centre. As a well-studied object, its broad-line region size has been measured via H $\rm {\alpha }$ time lag in numerous spectroscopic reverberation mapping (SRM) and narrow-band photometric reverberation mapping (PRM) campaigns. Here, we present its H $\rm {\alpha }$ time lag measurement using broad-band photometric data, with the application of our newly developed ICCF-Cut (Interpolation and Cross-Correlation Function - Cut) method as well as the javelin (Just Another Vehicle for Estimating Lags In Nuclei) and χ2 methods. Utilizing the minute-cadence multiband light curves obtained from the $\rm {2}$-m Faulkes Telescope North and $\rm {10.4}$-m Gran Telescopio Canarias telescopes in recent works, we measured its H $\rm {\alpha }$ lag as approximately 40–90 min from broad-band PRM. With the H $\rm {\alpha }$ emission line velocity dispersion, we calculated its central black hole mass as $M_{\rm BH} = (8\pm 4) \times 10^3\ \mathrm{ M}_{\rm \odot }$. These results are comparable with previous results obtained by narrow-band PRM and SRM, providing further support to an intermediate-mass black hole in NGC 4395. In addition, our study also validates the ICCF-Cut as an effective method for broad-band PRM, which holds the potential for widespread application in the era of large multi-epoch, high-cadence photometric surveys.