ASCA detection of faint sources in the Lockman Hole and its comparison with ROSAT sources

We conducted the ASCA observations of the Lockman Hole, aiming to detect faint sources and to determine the CXB origin. We have detected 18 discrete sources in 5σ significance from 0.7-2/2–7/0.7-7 keV band images obtained with ASCA. Correlated with the ROSAT catalog, 13 sources out of 16 (2 are out of bounds) have counterparts in the catalog, and 11 are identified as AGNs. We further determined the ASCA counting rate for all cataloged ROSAT sources utilizing the source position in the ROSAT catalog. Correlation between ROSAT counts (0.5-2 keV) and ASCA counts (2–10 keV) shows a large scatter. This suggests time variability of sources and/or the various degree of absorption / soft-excess on the spectra of AGNs which contribute the CXB.