Optical Variability of "Light-weight" Supermassive Black Holes at a Few Percent Level from ZTF Forced-Photometry Light Curves

TL;DR

This paper introduces an algorithm to analyze ZTF light curves, enabling detection of weak AGN variability at 1-3% levels, which can substitute for costly X-ray observations.

Contribution

The authors developed a novel post-processing algorithm that filters out artefacts and trends, improving sensitivity to weak AGN variability in large photometric datasets.

Findings

Successfully detected broadband variability at 1-3% level in ZTF light curves.

Demonstrated that optical variability can serve as a proxy for X-ray follow-up.

Enhanced the ability to identify intermediate-mass black hole AGN using photometric data.

Abstract

Large time-domain surveys provide a unique opportunity to detect and explore variability of millions of sources on timescales from days to years. Broadband photometric variability can be used as the key selection criteria for weak type-I active galactic nuclei (AGN), when other "direct" confirmation criteria like X-ray or radio emission are unavailable. However, to detect variability of rather weak AGN powered by intermediate-mass black holes, typical sensitivity provided by existing light curve databases is insufficient. Here we present an algorithm for post-processing of light curves for sources with stochastic variability, retrieved from the The Zwicky Transient Facility (ZTF) Forced Photometry service. Using our approach, we can filter out spurious data points related to data reduction artefacts and also eliminate long-term trends related to imperfect photometric calibration. We can now confidently detect the broad-band variability at the 1-3 $\%$ level which can potentially be used as a substitute for expensive X-ray follow-up observations.