Mining the XRT archive to probe the X-ray absorber structure in the AGN population

TL;DR

This study analyzes the Swift-XRT archive to investigate the structure and variability of X-ray absorbers in AGN, aiming to better understand the circumnuclear medium around supermassive black holes.

Contribution

It introduces a novel approach of mining archival data to identify AGN with extreme X-ray column density variability and presents new monitoring results for Mrk 915.

Findings

Identified AGN with significant column density variability.

Provided constraints on the size and location of X-ray absorbers.

Discovered new candidate AGN exhibiting extreme variability.

Abstract

One of the key ingredients of the Unified Model of Active Galactic Nuclei (AGN) is the presence of a torus-like optically thick medium composed by dust and gas around the putative supermassive black hole. However, the structure, size and composition of this circumnuclear medium are still matter of debate. To this end, the search for column density variations through X-ray monitoring on different timescales (months, weeks and few days) is fundamental to constrain size, kinematics and location of the X-ray absorber(s). Here we describe our project of mining the Swift-XRT archive to assemble a sample of AGN with extreme column density variability and determining the physical properties of the X-ray absorber(s). We also present the results obtained from a daily-weekly Swift-XRT follow-up monitoring recently performed on one of the most interesting new candidates for variability discovered so far, Mrk 915.