The XMM-Newton view of IRAS 09104+4109: evidence for a changing-look Type 2 quasar?

TL;DR

This study analyzes X-ray data of IRAS 09104+4109, suggesting it may be a changing-look quasar with variable absorption properties, based on evidence from XMM-Newton and BeppoSAX observations.

Contribution

It provides the first evidence that IRAS 09104+4109 could be a changing-look quasar with variable line-of-sight absorption, based on multi-epoch X-ray analysis.

Findings

The quasar's X-ray emission is dominated by intra-cluster medium thermal emission.

Both transmission and reflection models fit the data well, indicating complex absorption.

The absorber may have changed from Compton-thick to Compton-thin over five years.

Abstract

We analyzed the spectroscopic data from the PN and the MOS cameras in the 0.4-10 keV band. We also used an archival BeppoSAX 1-50 keV observation of IRAS 09104+4109 to investigate possible variations of the quasar emission. The X-ray emission in the EPIC band is dominated by the intra-cluster medium thermal emission. We found that the quasar contributes ~35% of the total flux in the 2-10 keV band. Both a transmission- (through a Compton-thin absorber with a Compton optical depth of \tau_C~0.3, i.e. Nh~5 x 10^{23} cm^-2) and a reflection-dominated (\tau_C>1) model provide an excellent fit to the quasar continuum emission. However, the value measured for the EW of Fe Kalpha emission line is only marginally consistent with the presence of a Compton-thick absorber in a reflection-dominated scenario, which had been suggested by a previous, marginal (i.e. 2.5\sigma) detection with the hard X-ray (15-50 keV), non-imaging BeppoSAX/PDS instrument. Moreover, the value of luminosity in the 2-10 keV band measured by the transmission-dominated model is fully consistent with that expected on the basis of the bolometric luminosity of IRAS 09104+4109. From the analysis of the XMM-Newton data we therefore suggest the possibility that the absorber along the line of sight to the nucleus of IRAS 09104+4109 is Compton-thin. Alternatively, the absorber column density could have changed from Compton-thick to -thin in the five years elapsed between the observations. If this is the case, then IRAS 09104+4109 is the first 'changing-look' quasar ever detected.