2000A&A...353..910F

We studied with BeppoSAX the infrared luminous galaxy IRAS 09104+4109 over a very wide X-ray band from 0.1 to 80keV. Our observations indicate the dominance of a thermal component at energies below 8keV, which we attribute to the free-free emission from the intracluster (IC) plasma surrounding the source. Above 10keV we find evidence for the existence of flux in excess with respect to the free-free IC plasma emission. This, together with the marginal detection of a neutral iron line at ∼6.4keV, gives a strong indication for the presence of an AGN deeply buried within the source. This component is best modelled by a strongly absorbed (N_H≥5x10²⁴cm^–2) power-law plus unabsorbed reflection spectrum (0.15≤R≤0.3), which is also responsible for the cold iron line. The unabsorbed broad-band (2-100keV) X-ray emission of this AGN is 2.5x10⁴⁶erg/s, well within the range of quasar luminosities. Our results indicate that IRAS 09104+4109 is indeed the prototype of a rare class of sources, the luminous type-2 QSOs. The association of this source with a huge cooling-flow of ∼1000M_☉ in the cluster, as indicated by the X-ray data, might suggest that such condition of extremely fast mass accumulation could favour the survival of a thick obscuring envelope, which would otherwise be quickly destroyed by the very luminous central source.