2023/07/05 by Miller, Jake A., Cackett, Edward M., Goad, Michael R. +9 · 2 citations
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2307.02630
Continuum reverberation mapping probes the sizescale of the optical continuum-emitting region in active galactic nuclei (AGN). Through 3 years of multiwavelength photometric monitoring in the optical with robotic observatories, we perform continuum reverberation mapping on Mrk~876. All wavebands show large amplitude variability and are well correlated. Slow variations in the light curves broaden the cross-correlation function (CCF) significantly, requiring detrending in order to robustly recover interband lags. We measure consistent interband lags using three techniques (CCF, JAVELIN, PyROA), with a lag of around 13~days from u to z. These lags are longer than the expected radius of 12~days for the self-gravitating radius of the disk. The lags increase with wavelength roughly following λ4/3, as would be expected from thin disk theory, but the lag normalization is approximately a factor of 3 longer than expected, as has also been observed in other AGN. The lag in the i band shows an excess which we attribute to variable Hα broad-line emission. A flux-flux analysis shows a variable spectrum that follows fν∝ λ-1/3 as expected for a disk, and an excess in the i band that also points to strong variable Hα emission in that band.