Comparison of high and low state X-ray spectra in the Type 1 QSO 2MASS 0918+2117

TL;DR

This study compares the X-ray spectra of the Type 1 QSO 2MASS 0918+2117 during low and high flux states, revealing changes in spectral shape, absorption, and reflection features over time.

Contribution

It provides the first detailed comparison of the source's X-ray spectral states, highlighting the variability and nature of the absorbing and reflecting material.

Findings

X-ray flux recovered in 2005 with typical spectral slope

Evidence of low ionisation state of absorbing gas

Presence of a soft excess similar to the 2003 observation

Abstract

When observed by XMM-Newton in 2003 the type 1 QSO 2MASS 0918+2117 was found to in a low flux state, some ~4-5 times fainter than during an earlier Chandra observation. The 2-6 keV spectrum was unusually hard, with evidence for a reflection-dominated continuum, while a soft excess prevented confirmation of the anticipated low energy absorber. In a second XMM-Newton observation in 2005, the X-ray flux is found to have recovered, with a 2-10 keV continuum slope now typical of broad-line active galaxy, and clear evidence for low energy absorption. We find the preferred ionisation state of the absorbing gas to be low, consistent with the red nucleus and strong optical polarisation of 2MASS 0918+2117. A residual soft excess is of similar spectral form and flux to that seen in 2003.