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R. Giacconi (AUI, JHU), P. Rosati (ESO), P. Tozzi, M. Nonino (OAT), G. Hasinger (AIP), C. Norman (JHU, STScI), J. Bergeron (ESO), S. Borgani (INFN), R. Gilli (Univ. Firenze), R. Gilmozzi (ESO), W. Zheng (JHU)
We present results from 300 ks of X-ray observations obtained with the Advanced CCD Imaging Spectrometer on the Chandra X-ray Observatory. We reach a flux of 10-16 erg s-1 cm-2 in the 0.5-2 keV soft band and 10-15 erg s-1 cm-2 in the 2-10 keV hard band. Our combined sample now reaches a total of over 200 sources in ~0.1 square degrees with S/N ~2.
We use the FORS-1 imaging-spectrometer for identifications, supplemented by the information obtained with the ESO Imaging Survey (EIS) and the ESO Wide Field Imager Survey (WFI). Positional accuracy is ~1'' in the central 6'. Optical spectra have been obtained for a small fraction of the sample.
Cumulative X-ray spectra for sources in the sample divided into broad flux bins show the hardening of the X-ray spectra at fainter fluxes. Hardness ratios for individual sources confirm this result and provide elements for classification.
We discuss the LogN-LogS relationship and the discrete source contribution to the integrated X-ray sky flux.
>From the U-band and the B-band dropouts we discuss the highest redshift objects in our sample.
We compare FX/Fopt of the sources observed in this survey to that of ROSAT and note a number of sources which appear to be galaxies that cluster at low FX/Fopt .
The R-K vs R color diagrams show a reddening of the Chandra sources with increasing magnitudes. A few objects have R-K > 6.
We compare our findings with previous results and with the predictions of models of the X-ray background. We show that Chandra is obtaining the predicted sensitivity and discuss the potential for even deeper surveys.