Spectrophotometric Reverberation Mapping of Intermediate-mass Black Hole NGC 4395

Abstract

Understanding the origins of massive black hole seeds and their coevolution with their host galaxy requires studying intermediate-mass black holes (IMBHs) and estimating their mass. However, measuring the masses of these IMBHs is challenging, due to the high-spatial-resolution requirement. Spectrophotometric reverberation monitoring is performed for a low-luminosity Seyfert 1 galaxy, NGC 4395, to measure the size of the broad-line region and black hole mass. The data were collected using the 1.3 m Devasthal fast optical telescope and 3.6 m Devasthal optical telescope at ARIES, Nainital, over two consecutive days in 2022 March. The analysis revealed strong emission lines in the spectra and light curves of the merged 5100 Å spectroscopic continuum flux ( f _5100 ) with the photometric continuum V band and H α , with fractional variabilities of 6.38% and 6.31% respectively. In comparison to several previous studies with lag estimation <90 minutes, our calculated H α lag supersedes them by ${125.0}_{-6.1}^{+6.2}$ minutes, using the ICCF and JAVELIN methods. The velocity dispersion ( σ _line ) of the broad-line clouds is measured to be ${544.7}_{-25.1}^{+22.4}$ km s ^−1 , yielding a black hole mass of ∼ ${2.2}_{-0.2}^{+0.2}\times {10}^{4}{M}_{\odot }$ and an Eddington ratio of 0.06.

Keywords

• Black holes
• Active galactic nuclei
• Reverberation mapping
• Spectroscopy
• Intermediate-mass black holes