A Spectral Energy Distribution Variability Study of the Eclipsing AGN NGC 6814

TL;DR

This study analyzes 10 years of optical-to-X-ray data of NGC 6814, revealing distinct variability patterns, eclipse-related X-ray weakness, and insights into the accretion disk structure around its supermassive black hole.

Contribution

It provides a multi-epoch spectral energy distribution analysis of NGC 6814, highlighting variability mechanisms and suggesting a non-standard accretion disk structure.

Findings

Distinct variability behaviors across epochs.

X-ray weakness linked to eclipses and absorption.

Accretion disk possibly larger than standard models.

Abstract

The local Seyfert 1.5 active galactic nucleus (AGN), NGC 6814, is known to exhibit complex variability, eclipses, and even changing-look behaviour. In this work, we utilize optical-to-X-ray data obtained over 10-years with the Neil Gehrels Swift Observatory to examine the short-term (i.e. daily) and long-term (yearly) variations in the spectral energy distribution (SED). This includes three epochs of high-cadence monitoring (2012, 2016, and 2022), as well as two single observations (2019 and 2021). Model-independent methods of examining the variability suggest that the three monitored epochs exhibit distinct behaviour. X-ray weakness in 2016 can be attributed to the previously studied eclipses, while similar behaviour in 2012 is associated with continuum changes and slight neutral absorption. The multi-epoch SED models are consistent with a black hole (log (MBH / Msun) ~7.6) that is accreting between 0.01-0.1 of the Eddington rate. While the corona (primary X-ray source) is compact, all epochs are better fit with an accretion disk inner radius that is much larger than the innermost stable circular orbit, implying the possibility of a non-standard accretion disk or central structure in NGC 6814.