The Extended Chandra Deep Field-South Survey: Optical Properties of   X-ray Detected Sources
  The Extended Chandra Deep Field-South (E-CDF-S) survey consists of 4 Chandra ACIS-I pointings and covers ~1100 square arcminutes (~0.3 deg^2) centered on the original CDF-S field to a depth of approximately 228 ks (PI: Niel Brandt; Lehmer et al, 2005). This is the largest Chandra survey ever conducted at such depth. In our analysis (Virani et al, 2005), we detect 651 unique sources -- 587 using a conservative source detection limit and 64 using a lower source detection limit. Of these 651 sources, 561 are detected in the full 0.5--8.0 keV band, 529 in the soft 0.5--2.0 keV band, and 335 in the hard 2.0--8.0 keV band. For point sources near the aim point, the limiting fluxes are approximately $1.7 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ and $3.9 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ in the 0.5--2.0 keV and 2.0--8.0 keV bands, respectively. We present the optical properties of these X-ray sources, specifically the R-band magnitude distribution and a preliminary spectroscopic redshift distribution. One exciting result is the discovery of 7 new Extreme X-ray-to-Optical flux ratio objects (EXOs) found in the E-CDF-S field. 
Shanil Virani (1), Ezequiel Treister (1,2), C. Megan Urry (1), Eric   Gawiser (1) and the MUSYC Collaboration ((1) Yale Univ...