New Results from the X-ray and Optical Survey of the Chandra Deep Field South: The 300ks Exposure
Abstract
We present results from 300 ks of X-ray observations of the Chandra Deep Field South. The field of the four combined exposures is now 0.1035 deg^2 and we reach a flux limit 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, thus a factor 2 fainter than the previous 120 ks exposure. The total catalogue is composed of 197 sources including 22 sources detected only in the hard band, 51 only in the soft band, and 124 detected in both bands. We have now the optical spectra for 84 optical counterparts. The LogN-LogS relationship of the whole sample confirms the previous finding that there is no significant flattening for the hard counts and some evidence of flattening of the soft counts. We compute the total contribution to the X-ray background in the 2-10 keV band, which now amounts to (1.45 +- 0.15) 10^{-11} erg cm^{-2} s^{-1} deg^{-2} (after the inclusion of the ASCA sources to account for the bright end), to a lower flux limit of 10^{-15} erg s^{-1} cm^{-2}. This corresponds to 60-90% of the unresolved hard X-ray background (XRB), given the uncertainties of its actual value. We confirm our previous finding on the average spectrum of the sources and the progressive hardening of the sources at lower fluxes. In particular we find that the average slope of the sources is flatter (relative to a photon index \Gamma = 1.4) for fluxes lower than 9 10^{-15} erg s^{-1} cm^{-2} in the hard band [ABRIDGED].Keywords
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