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 � 1024 cm?2 while the line-of-sight column density to be ?7-8 � 1023 cm-2. The source is found to be deeply buried with the torus covering factor of ?0.85. We observe variability in the line-of-sight column density on a time-scale of <35 d. 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.