ROSAT EXTENDED MEDIUM-DEEP SENSITIVITY SURVEY - SOURCE COUNTS FOR 130 FIELDS

We present an analysis of serendipitous sources detected in 130 high Galactic latitude, long-exposure ROSAT PSPC observations. By application of an efficient source detection technique and analyzing a larger number of fields compared to previous studies, we have sufficiently increased the sky coverage of the survey and are able to investigate the X-ray source population over almost three decades of intensity, from approximately 1.2 x 10(-15) to approximately 7.0 x 10(-13) ergs s(-1) cm(-2) in the 0.5-2.0 keV energy band. Using the 2678 detected sources, we refine the extragalactic log N-log S and find that the differential number-flux relation is well described by a broken power law which flattens from alpha = 2.55 +/- 0.08 above a flux of 2.2 +/- 0.2 x 10(-14) ergs s(-1) cm(-2) to 1.86 +/- 0.06 at fainter fluxes, which is in a good agreement with previous studies. At our limiting flux of 1.2 x 10(-15) ergs s(-1) cm(-2), the detected (point) sources comprise 66 +/- 7% (68% confidence limits) of the X-ray background in the 1-2 keV band.