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