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RAY BRIGHT OPTICALLY NORMAL GALAXIES

Multiwavelength observations of the hard X–ray selected sources by Chandra and XMM–Newton surveys have significantly improved our knowledge of the objects responsible of the hard X–ray background. A surprising finding is the discovery of a population of optically dull, X–ray bright galaxies emerging at 2–10 keV fluxes of the order of 10 erg cm s. We present preliminary results of multiwavelength observations of a few objects serendipitously discovered in the field of XMM–Newton and Chandra observations and intensively studied at longer wavelengths.