BeppoSAX uncovers a type-2 QSO in the hyperluminous infrared galaxy IRAS 09104+4109

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 dom inance of a thermal component at energies below 8 keV, which we attribute t o the free-free emission from the intracluster (IC) plasma surrounding the source. Above 10keV we find evidence for the existence of flux in excess wi th respect to the free-free IC plasma emission. This, together with the mar ginal detection of a neutral iron line at N 64keV, gives a strong indicatio n for the presence of an AGN deeply buried within the source. This componen t is best modelled by a strongly absorbed (NH greater than or equal to 5 x 10(24)cm(-2)) power-law plus unabsorbed reflection spectrum (0.15 less than or equal to R less than or equal to 0.3), which is also responsible for th e cold iron line. The unabsorbed broad-band (2-100 keV) X-ray emission of t his AGN is 2.5 x 10(46) erg s(-1), well within the range of quasar luminosi ties. 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-how of similar to 1000 M., in the cluster, as in dicated by the X-ray data, might suggest that such condition of extremely f ast mass accumulation could favour the survival of a thick obscuring envelo pe, which would otherwise be quickly destroyed by the very luminous central source.