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The contribution of faint AGN to the hard X-ray background

F. Fiore·F. La Franca·P. Giommi·M. Elvis·G. Matt·A. Comastri·S. Molendi·I. Gioia
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Abstract

Hard X-ray selection is the most efficient way to discriminate between accretion-powered sources, such as AGN, from sources dominated by starlight. Hard X-rays are also less affected than other bands by obscuration. We have then carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5-10 keV band, finding 180 sources in ~50 deg^2 of sky with flux >5E-14 erg cm-2 s-1. After correction for the non uniform sky coverage this corresponds to resolving about 30 % of the hard Cosmic X-ray Background (XRB). Here we report on a first optical spectroscopic identification campaign, finding 12 AGN out of 14 X-ray error-boxes studied. Seven AGN show evidence for obscuration in X-ray and optical bands, a fraction higher than in previous ROSAT or ASCA-ROSAT surveys (at a 95-99 % and 90 % confidence level respectively), thus supporting the scenario in which a significant fraction of the XRB is made by obscured AGN.

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F. Fiore, F. La Franca, P. Giommi, M. Elvis, G. Matt, A. Comastri, S. Molendi, I. Gioia. 1999-03-30. The contribution of faint AGN to the hard X-ray background. https://doi.org/10.1046/j.1365-8711.1999.02795.x

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