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Description
We have performed a moderately deep soft X-ray (0.1-2keV) survey of the Galactic plane using pointed observations with the ROSAT Position Sensitive Proportional Counter (PSPC). The survey is more than an order of magnitude more sensitive than previous X-ray surveys near the Galactic plane. The data consist of nine fields each of ~10ks exposure, pointed at positions on or very close to the Galactic plane (|b|<0.3{deg}) in the longitude range 180{deg}<~l<~280{deg}. This region has relatively low X-ray absorbing material out to distances of several hundred pc and presents fewer source-confusion problems than at other longitudes. The total sky area surveyed was 2.5deg^2^ this yielded 93 sources, 89 of which were detected in the hard (0.4-2.0keV) band. Nine sources were detected in both soft (0.1-0.4keV) and hard bands. In the hard band, the survey coverage is 90 per cent for sources brighter than 0.002count/s (~2x10^-14^erg/cm^2^/s), but falls steeply below this value, with the weakest sources being ~0.001count/s. The median limiting flux is <~0.0013count/s (~1.3x10^14^erg/cm^2^/s). There are 64 sources with hard-band count rates >0.002count/s. We present the catalogue of X-ray sources and the number-flux relations (logN-logS). Eighteen sources have possible identifications from the SIMBAD data base. We have searched the Tycho-2 (Cat. <I/259>) and USNO-A2.0 (Cat. <I/252>) catalogues to find all possible optical counterparts brighter than 19th magnitude, and attempt to classify these on the basis of log(FX/Fopt) versus optical colour diagrams and near-infrared photometry from the 2MASS Second Incremental Data Release (Cat. <B/2mass>). Hence, we have found the majority of these sources to be consistent with being late-type main-sequence stars, as previous studies have proposed from incompletely identified surveys. Comparison of the measured number-flux relations with predictions of Galactic (stellar) and extragalactic populations supports the view that the population of young stars in the plane is denser than previously thought.
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