A long hard look at the minimum state of PG 2112+059 with XMM-Newton

TL;DR

This study analyzes the X-ray spectral variability of quasar PG 2112+059 using XMM-Newton data, exploring reflection and absorption models, and constraining black hole spin through light bending effects.

Contribution

It provides a detailed spectral analysis of PG 2112+059 in different flux states, comparing reflection and absorption scenarios, and constrains the black hole spin using light bending models.

Findings

Detection of a weak iron fluorescent line indicating distant reflection.

Spectral variability explained by ionized absorption layers and reflection models.

Black hole spin constrained to a/M > 0.86 using light bending models.

Abstract

XMM-Newton successfully detected the minimum state of PG 2112+059 during a short snapshot observation and performed a long follow-up observation. The high signal-to-noise spectra are modelled assuming different emission scenarios and compared with archival spectra taken by XMM-Newton and Chandra. The PG 2112+059 X-ray spectra acquired in May 2007 allowed the detection of a weak iron fluorescent line, which is interpreted as being caused by reflection from neutral material at some distance from the primary X-ray emitting source. The X-ray spectra of PG 2112+059 taken at five different epochs during different flux states can be interpreted within two different scenarios. The first consists of two layers of ionised material with column densities of N_H ~5 x 10^22 cm^-2 and N_H ~3.5 x 10^23 cm^-2, respectively. The first layer is moderately ionised and its ionisation levels follow the flux changes, while the other layer is highly ionised and does not show any correlation with the flux of the source. The spectra can also be interpreted assuming reflection by an ionised accretion disk seen behind a warm absorber. The warm absorber ionisation is consistent with being correlated with the flux of the source, which provides an additional degree of self-consistency with the overall reflection-based model. We explain the spectral variability with light bending according to the models of Miniutti and Fabian and constrain the black hole spin to be a/M > 0.86. Both scenarios also assume that a distant cold reflector is responsible for the Fe K \alpha emission line. Light bending provides an attractive explanation of the different states of PG 2112+059 and may also describe the physical cause of the observed properties of other X-ray weak quasars.