Abstract. We present results from the photometric and spectroscopic identification of 122 X-ray sources recently discovered by XMM-Newton in the 2-10 keV band (the HELLAS2XMM 1dF sample). Their flux cover the range 8 × 10 −15 −4 × 10 −13 erg cm −2 s −1 and the total area surveyed is 0.9 square degrees. One of the most interesting results (which is found also in deeper sourveys) is that about 20% of the hard X-ray selected sources have an X-ray to optical flux ratio (X/O) ten times or more higher than that of optically selected AGN. Unlike the faint sources found in the ultra-deep Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes more than one order of magnitude lower than the HELLAS2XMM survey sources, many of the extreme X/O sources in our sample have R < ∼ 25 and are therefore accessible to optical spectroscopy. We report the identification of 13 sources with X/O > ∼ 10 (to be compared with 9 sources known from the deeper, pencil-beam surveys). Eight of them are narrow line QSO (seemingly the extension to very high luminosity of the type 2 Seyfert galaxies), four are broad line QSO. The results from our survey are also used to make reliable predictions about the luminosity of the sources not yet spectroscopically identified, both in our sample and in deeper Chandra and XMM-Newton samples. We then use a combined sample of 317 hard X-ray selected sources (HELLAS2XMM 1dF, Chandra Deep Field North 1Msec, Chandra SSA13 and XMM-Newton Lockman Hole flux limited samples), 221 with measured redshifts, to evaluate the cosmological evolution of the hard X-ray source's number and luminosity densities. Looking backward in time, the low luminosity sources (log L 2−10 keV = 43−44 erg s −1 ) increase in number at a much slower rate than the very high luminosity sources (log L 2−10 keV > 44.5 erg s −1 ), reaching a maximum around z = 1 and then levelling off beyond z = 2. This translates into an accretion driven luminosity density which is dominated by sources with log L 2−10 keV < 44.5 erg s −1 up to at least z = 1, while the contribution of the same sources and of those with log L 2−10 keV > 44.5 erg s −1 appear, with yet rather large uncertainties, to be comparable between z = 2 and 4.

We present an occultation of the central X-ray emitting region in the Seyfert Galaxy NGC 1365. This extreme spectral variation (from Compton-thin to reflection-dominated and back to Compton-thin in four days) has been caught in a ten days Chandra monitoring campaign consisting of six short (15 ks) observations performed every two days. We discuss the implications of this occultation within the scenario of a Compton-thick cloud crossing the line of sight of the X-ray source. We estimate a source size R ≤ 10 14 cm and a distance of the cloud from the source D ≤ 10 16 cm. This direct measurement confirms the theoretical expectations of an extremely compact X-ray source, and shows that the Compton-thick circumnuclear gas is located at a distance from the center on the scale of the Broad Line Region.

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We present the first results from an XMM-Newton serendipitous medium-deep survey, which covers nearly three square degrees. We detect a total of 1022, 495 and 100 sources, down to minimum fluxes of about 5.9 × 10 −16 , 2.8 × 10 −15 and 6.2 × 10 −15 erg cm −2 s −1 , in the 0.5-2, 2-10 and 4.5-10 keV band, respectively. In the soft band this is one of the largest samples available to date and surely the largest in the 2-10 keV band at our limiting X-ray flux. The measured Log(N)-Log(S) are found to be in good agreement with previous determinations. In the 0.5-2 keV band we detect a break at fluxes around 5 × 10 −15 erg cm −2 s −1 . In the harder bands, we fill in the gap at intermediate fluxes between deeper Chandra and XMM-Newton observations and shallower BeppoSAX and ASCA surveys.