A deep ROSAT survey of the Lynx area

The results of the optical spectroscopic follow-up to a deep ROSAT (Röntgen Satellite) Survey in the Lynx area are presented. The best optical candidates for the X-ray sources taken with the Kitt Peak 4 meter Hydra multi-fiber spectrograph and the Multiple Mirror Telescope's Red Channel are presented. Of the 72 ROSAT X-ray sources flux-limited here, 68 have had at least one optical candidate observed spectroscopically: 58 reliable identifications have been made, and the remaining 10 spectra are unclassified leaving a total of 14 X-ray sources without secure optical identifications. The identifications are 22 stars, 20 galaxies, and 16 quasars. The fraction of stellar identifications is >= 25%, which is attributed to the incomplete spectral coverage (only completely down to Gunn-r ~ 19 mag) of the optical catalog, which reaches Gunn-r ~ 25 mag. A review of the collected X-ray data is given. Most sources have hard (0.4-2.4 keV) spectra, four are rather soft (0.1-0.4 keV), and two seem to be extended X-ray sources. The observed ROSAT X-ray source counts in Lynx have a slope and amplitude consistent with those of the Einstein Medium Sensitivity (EMSS) and the Einstein Deep Surveys. Around S_X ~ 10^-14 ergs cm^{- 2} s^-1, our counts appear to flatten, in agreement with the results of the ROSAT Extended Medium-Deep Sensitivity and Lockman field surveys. Below this level and to our 3.5σ completeness limit, the observed counts have a slope of 1.1 +/- 0.2. After correction for ``Eddington bias'', our inferred intrinsic slope is 0.9 +/- 0.2, a value (at least marginally) flatter than the EMSS slope of 1.48 +/- 0.05 appropriate at brighter X-ray fluxes. A comparison of the flux ratios (X-ray to optical) for this deep ROSAT Survey's galaxies and quasi-stellar objects (QSO) agrees fairly well with those for the EMSS. Follow-up work will include completion of the optical spectroscopic follow-up so that the bias from the stellar identifications can be overcome, and constraining the trivariate (radio-optical-X-ray) luminosity function.