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J.M. Vrtilek (CfA), D. Freedman (Princeton), W. Forman, C. Jones, L. Grego, L. VanSpeybroeck, S. Virani (CfA)
We present an analysis of point sources serendipitously found in two deep Chandra exposures with ACIS-I that were originally obtained to observe clusters of galaxies at high redshifts: MS1137.5+6625 (120 ks) and CL0848.6+4453 (190 ks). Sources, detected with a wavelet-based algorithm, were identified to a limiting flux of about 2 \times 10-16 erg~cm-2~s-1, at which their density reaches 1700 sources~deg-2. LogN~--~logS plots are approximately consistent with those obtained from earlier missions and extend these to lower fluxes. We confirm earlier results that show a hardening of spectra at lower fluxes, and discuss implications for the nature and evolution of the sources and for our understanding of the X-ray background.