Changing look AGN Mrk 590: broad-line region and black hole mass from photometric reverberation mapping

Abstract

ABSTRACT We present the results of photometric reverberation mapping observations on the changing look active galactic nucleus Mrk 590 at z = 0.026. The observations were carried out from 2018 July to December using broad-bandB-,R-, and narrow-band H α and S ii filters. The B band traces the continuum emission from the accretion disc, the R band encompasses both the continuum emission from the accretion disc and the redshifted H α line from the broad-line region (BLR), the S ii band contains the redshifted H α emission and the H α band traces the continuum emission underneath the S ii band. All the light curves showed strong variation with a fractional root-mean-square variation of 0.132 ± 0.001 in the B band and 0.321 ± 0.001 in H α line. From cross-correlation function analysis, we obtained a delayed response of H α line emission to the opticalB-band continuum emission of $21.44^{+1.49}_{-2.11}$ d in the rest frame of the source, corresponding to a linear size of the BLR of 0.018 pc. This is consistent with previous estimates using H β. By combining the BLR size with the H α line full width at half-maximum of 6478 ± 240 km s−1 measured from a single-epoch spectrum obtained with the Subaru telescope, we derived a black hole mass of $1.96^{+0.15}_{-0.21}\times 10^8 {\rm M}_{\odot }$.