Black hole spin and size of the X-ray emitting region(s) in the Seyfert 1.5 galaxy ESO 362-G18

TL;DR

This study analyzes multi-epoch X-ray data of Seyfert galaxy ESO 362-G18, revealing a rapidly spinning black hole and constraining the size of the X-ray emitting region to within approximately 50 gravitational radii.

Contribution

First measurement of black hole spin and X-ray emitting region size in ESO 362-G18 using reflection modeling and absorption variability analysis.

Findings

Black hole spin ≥ 0.92 at 99.99% confidence

X-ray emitting region within ~50 gravitational radii

Absorption variability linked to a clumpy dusty torus

Abstract

We report results from multi-epoch X-ray observations of the Seyfert 1.5 galaxy ESO 362-G18 performed between November 2005 and June 2010. ESO 362-G18 generally exhibits the typical X-ray spectrum of type 1 Active Galactic Nuclei (AGN). A disc-reflection component accounts for broad residuals in the iron K band and above 10~keV, as well as for a significant soft excess. From our best-fitting reflection model, we measure a black hole spin greater or equal to 0.92 at the 99.99 per cent confidence level. ESO 362-G18 is also (typically) mildly absorbed by a column of neutral gas. The absorber is variable and one observation, performed ~2 months after a typical mildly absorbed one, is heavily absorbed by a cold column density two orders of magnitude higher than that during any other observation. UV variability between the heavily absorbed observation and the others suggests that the absorber can be identified with a dusty, clumpy torus. The absorption variability timescale enables us to locate the X-ray emitting region within the innermost ~50 gravitational radii. Such result holds not only for the X-ray continuum, but also for the soft excess.