A multi-epoch X-ray study of the nearby Seyfert 2 galaxy NGC 7479: Linking column density variability to the torus geometry

TL;DR

This study analyzes multi-epoch X-ray data of NGC 7479 to investigate the structure and variability of its obscuring torus, providing insights into cloud distribution and torus geometry in Seyfert 2 galaxies.

Contribution

It offers the first detailed multi-epoch analysis linking column density variability to the torus structure and cloud distribution in NGC 7479.

Findings

Detected variability in hydrogen column density indicating a patchy torus.

Estimated the cloud distance from the central black hole.

Determined the Eddington ratio to be between 0.04 and 0.05.

Abstract

Active galactic nuclei (AGN) are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. Recent studies have shown how the torus structure, formerly thought to be homogeneous, appears to be 'patchy': the detection of variability in the line-of-sight hydrogen column density, in fact, matches the description of an obscurer with a complex structure made of clouds with different column density. In this work, we perform a multi-epoch analysis of the X-ray spectra of the Seyfert 2 galaxy NGC 7479 in order to estimate its torus properties, such as the average column density and the covering factor. The measurement of the line-of-sight hydrogen column density variability of the torus allows us to obtain an upper limit on the cloud distance from the central engine. In addition, using the X-ray luminosity of the source, we estimate the Eddington ratio to be in a range of Edd=0.04-0.05 over all epochs.