ROSAT Extended Medium-Deep Sensitivity Survey: Average Source Spectra

Details ROSAT Extended Medium-Deep Sensitivity Survey: Average Source Spectra ROSAT Extended Medium-Deep Sensitivity Survey: Average Source Spectra

Oct 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...451..564v&link_type=abstract

Astrophysical Journal v.451, p.564

Astronomy and Astrophysics

Astronomy

29

Surveys, X-Rays: Galaxies

Scientific paper

We present a spectral analysis of the serendipitous sources detected in 130 high Galactic latitude, long-exposure ROSA T PSPC observations. By application of an efficient source detection technique and analyzing a large number of fields, we have detected 2678 sources above our limiting flux of 1.2 × 1015 ergs s-1 cm-2 (see Papers I and II).
In this paper, we investigate the spectral properties of the detected sources. Analysis of hardness ratios as a function of flux confirms the suggestion in the recent work of Hasinger et al. that the source spectra show a hardening as the source fluxes decrease. Quantitatively, the hardness ratios are equivalent to a power-law energy index of 0.7 at a flux of 6 × 10-15 ergs s-1 cm-2. In addition to analyzing mean hardness ratios, we performed detailed spectral fits to the average pulse-height data of the sources as a function of flux. We find that at fluxes above 2 × 10-14 ergs s-1 cm-2, the average spectrum has a best-fit power-law energy index of 1.4 (after accounting for a Galactic stellar component). The best-fit power-law exponent decreases smoothly to 0.4 below a flux of 10-14 ergs -1 cm-2. This average spectrum of the faintest sources approaches that observed for the 2-10 keV X-ray background. We discuss the implications of measurements of the source counts and average spectra for models of the origin of the X-ray background.

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