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

TL;DR

This study uses photometric reverberation mapping to measure the size of the broad line region and estimate the black hole mass in the changing look AGN Mrk 590, demonstrating the method's effectiveness in variable AGN.

Contribution

First application of photometric reverberation mapping to a changing look AGN to determine BLR size and black hole mass.

Findings

BLR size of 0.018 pc measured from Hα line response

Black hole mass estimated at approximately 2 x 10^8 solar masses

Strong variability observed in optical and Hα light curves

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 July to December, 2018 using broad band B, R and narrow band H{\alpha} and S II filters. B-band traces the continuum emission from the accretion disk, R-band encompasses both the continuum emission from the accretion disk and the redshifted H{\alpha} line from the broad line region (BLR), S II band contains the redshifted H{\alpha} emission and the H{\alpha} 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 B-band and 0.321 (+/-) 0.001 in H{\alpha} line. From cross-correlation function analysis, we obtained a delayed response of H{\alpha} line emission to the optical B-band continuum emission of 21.44(+1.49/-2.11) days 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{\beta}. By combining the BLR size with the H{\alpha} line full width at half maximum of 6478 (+/-) 240 km/s measured from a single-epoch spectrum obtained with the Subaru telescope, we derived a black hole mass of 1.96 (+0.15 / -0.21) X 10^8 Msun.