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Astron. Astrophys. 353, 910-916 (2000)


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

A. Franceschini 1, L. Bassani 2, M. Cappi 2, G.L. Granato 3, G. Malaguti 2, E. Palazzi 2 and M. Persic 4

1 Dipartimento di Astronomia, Vicolo Osservatorio 5, 35122 Padova, Italy (franceschini@pd.astro.it)
2 ITeSRE/CNR, via Gobetti 101, 40129 Bologna, Italy
3 Osservatorio Astronomico, Vicolo Osservatorio 5, 35122 Padova, Italy
4 Osservatorio Astronomico, Via G. Tiepolo 11, 34131 Trieste, Italy

Received 15 July 1999 / Accepted 3 September 1999

Abstract

We studied with BeppoSAX the infrared luminous galaxy IRAS 09104+4109 over a very wide X-ray band from 0.1 to 80 keV. Our observations indicate the dominance of a thermal component at energies below 8 keV, which we attribute to the free-free emission from the intracluster (IC) plasma surrounding the source. Above 10 keV 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 [FORMULA] keV, gives a strong indication for the presence of an AGN deeply buried within the source. This component is best modelled by a strongly absorbed ([FORMULA] [FORMULA] 5 [FORMULA] 1024 cm-2) power-law plus unabsorbed reflection spectrum (0.15 [FORMULA] R [FORMULA] 0.3), which is also responsible for the cold iron line. The unabsorbed broad-band (2-100 keV) X-ray emission of this AGN is 2.5 [FORMULA] 1046 erg s-1, 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 [FORMULA] 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.

Key words: X-rays: galaxies – galaxies: active – galaxies: individual: IRAS 09104+4109

Send offprint requests to: A. Franceschini

© European Southern Observatory (ESO) 2000

Online publication: January 18, 2000

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