Accretion Disk Sizes from Continuum Reverberation Mapping of AGN Selected from the ZTF Survey

TL;DR

This study estimates accretion disk sizes in 19 AGN using ZTF light curves, finding sizes larger than standard models predict and weak correlations with SMBH mass and luminosity, advancing understanding of disk physics.

Contribution

Introduces a method to measure AGN accretion disk sizes using multi-band reverberation mapping with ZTF data, revealing larger-than-expected disk sizes and weak parameter correlations.

Findings

Disk sizes are on average 3.9 times larger than standard model predictions.

Interband lags are consistent with disk reprocessing expectations.

Weak correlation between disk size and SMBH mass/luminosity.

Abstract

We present the accretion disk size estimates for a sample of 19 active galactic nuclei (AGN) using the optical $g$, $r$, and $i$ band light curves obtained from the Zwicky Transient Facility (ZTF) survey. All the AGN have reliable supermassive black hole (SMBH) mass estimates based on previous reverberation mapping measurements. The multi-band light curves are cross-correlated, and the reverberation lag is estimated using the Interpolated Cross-Correlation Function (ICCF) method and the Bayesian method using the {\sc javelin} code. As expected from the disk reprocessing arguments, the $g-r$ band lags are shorter than the $g-i$ band lags for this sample. The interband lags for all, but 5 sources, are larger than the sizes predicted from the standard Shakura Sunyaev (SS) analytical model. We fit the light curves directly using a thin disk model implemented through the {\sc javelin} code to get the accretion disk sizes. The disk sizes obtained using this model are on an average 3.9 times larger than the prediction based on the SS disk model. We find a weak correlation between the disk sizes and the known physical parameters, namely, the luminosity and the SMBH mass. In the near future, a large sample of AGN covering broader ranges of luminosity and SMBH mass from large photometric surveys would be helpful in a better understanding of the structure and physics of the accretion disk.