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

¹ Osservatorio Astronomico di Roma (INAF), via Frascati 33, 00040 Monteporzio Catone (Roma), Italy e-mail: piconcelli@oa-roma.inaf.it
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
⁴ Max Planck Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
⁵ Osservatorio Astronomico di Bologna (INAF), via Ranzani 1, 40127 Bologna, Italy
⁶ ASI Science Data Center, ESRIN, via G. Galilei, 00044 Frascati, Italy

Received: 11 April 2007
Accepted: 6 July 2007

Abstract

Aims.We report on a 14 ks XMM-Newton observation of the hyperluminous infrared galaxy IRAS 09104+4109, which harbors a type 2 quasar in its nucleus. Our analysis was aimed at studying the properties of the absorbing matter and the Fe K complex at 6–7 keV in this source.

Methods.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.

Results.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 , i.e. N_H  cm^-2) and a reflection-dominated () model provide an excellent fit to the quasar continuum emission. However, the value measured for the EW of Fe Kα 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. 2.5σ) 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.