Unveiling the physics of low luminosity AGN through X-ray variability: LINER versus Seyfert 2

TL;DR

This study compares X-ray variability and spectral properties of LINER and Seyfert 2 AGN, revealing similarities in their nuclear continuum variations but differences in UV variability and accretion mechanisms, suggesting structural distinctions.

Contribution

It provides a comparative analysis of X-ray and UV variability in LINERs and Seyfert 2s, highlighting differences in luminosity, accretion, and obscuration, and proposing implications for AGN structure.

Findings

Seyfert 2s have higher X-ray luminosities and Eddington ratios.

Long-term X-ray variations are common in both LINERs and Seyfert 2s.

UV variations are detected in LINERs but not in Seyfert 2s.

Abstract

X-ray variability is very common in active galactic nuclei (AGN), but these variations may not occur similarly in different families of AGN. We aim to disentangle the structure of low ionization nuclear emission line regions (LINERs) compared to Seyfert 2s by the study of their spectral properties and X-ray variations. We assembled the X-ray spectral parameters and variability patterns, which were obtained from simultaneous spectral fittings. Major differences are observed in the X-ray luminosities, and the Eddington ratios, which are higher in Seyfert 2s. Short-term X-ray variations were not detected, while long-term changes are common in LINERs and Seyfert 2s. Compton-thick sources generally do not show variations, most probably because the AGN is not accesible in the 0.5--10 keV energy band. The changes are mostly related with variations in the nuclear continuum, but other patterns of variability show that variations in the absorbers and at soft energies can be present in a few cases. We conclude that the X-ray variations may occur similarly in LINERs and Seyfert 2s, i.e., they are related to the nuclear continuum, although they might have different accretion mechanisms. Variations at UV frequencies are detected in LINER nuclei but not in Seyfert 2s. This is suggestive of at least some LINERs having an unobstructed view of the inner disc where the UV emission might take place, being UV variations common in them. This result might be compatible with the disappeareance of the torus and/or the broad line region in at least some LINERs.