Impact of Baseline, Cadence, and Host Contamination on AGN Variability Metrics: A Systematic Study with ZTF

TL;DR

This study evaluates the stability of two AGN variability metrics, J and s, against observational factors like baseline, cadence, and host contamination, using ZTF data.

Contribution

It provides a systematic analysis of how baseline, cadence, and host contamination affect the reliability of variability metrics J and s in AGN studies.

Findings

J is robust to baseline variations and host contamination after subtraction.

s is sensitive to cadence and increases with host subtraction.

J remains stable across different observational conditions, s varies significantly.

Abstract

Variability in active galactic nuclei (AGN) probes the physics of accretion onto supermassive black holes. This variability is characterized using metrics derived from the flux distributions of temporally separated epochs. We studied the stability of two variability metrics, the Stetson index "J" and the smoothness "s", against baseline, cadence, and host galaxy contamination. We studied 23 nearby AGNs using Zwicky Transient Facility's Data Release 24. Both metrics are robust to baseline variations of $\sim 2$ years. However, s is sensitive to cadence, showing variations $\gtrsim 40\%$, while J shows minor variations $\lesssim10\%$. We studied the host galaxy impact using Mrk 493 as a representative case. We found that J remains unchanged after host subtraction, while s increases. We concluded that J is a robust tool for characterizing AGN variability, while s should be interpreted with caution.