Absorption variability of the highly obscured active galactic nucleus NGC 4507

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.