Absorption Variability of the Highly Obscured Active Galactic Nucleus NGC 4507

TL;DR

This study analyzes the X-ray absorption variability of the obscured active galaxy NGC 4507 using NuSTAR data, revealing stable primary emission but variable line-of-sight absorption likely from the BLR or torus.

Contribution

It provides detailed modeling of the obscuring material and its variability, offering new insights into the structure of the AGN's circumnuclear environment.

Findings

Primary X-ray emission is non-variable, indicating stable accretion.

Line-of-sight column density varies on timescales of less than 35 days.

The torus covering factor is approximately 0.85, consistent with recent surveys.

Abstract

We present a detailed study of the highly obscured active galaxy NGC 4507, performed using four Nuclear Spectroscopic Telescope Array (NuSTAR) observations carried out between May and August in 2015 (~ 130 ks in total). Using various phenomenological and physically motivated torus models, we explore the properties of the X-ray source and those of the obscuring material. The primary X-ray emission is found to be non-variable, indicating a stable accretion during the period of the observations. We find the equatorial column density of the obscuring materials to be ~ 2 x 10^24 cm^-2 while the line of sight column density to be ~ 7 - 8 x 10^23 cm^-22. The source is found to be deeply buried with the torus covering factor ~ 0.85. We observe variability in the line-of-sight column density on a timescale of < 35 days. The covering factor of the Compton-Thick material is found to be ~ 0.35, in agreement with the results of recent X-ray surveys. From the variability of the line-of-sight column density, we estimate that the variable absorbing material is likely located either in the BLR or in the torus.