The high spatial resolution of the HRI enabled
the identification of 94 HRI sources with well known objects based on the
positional coincidence and considering their extent and hardness
ratios. The coordinates of most of the identified
sources could be improved to more accurate positions and allowed the
positional correction of other HRI sources. Thus for 254 sources the
systematic error for their coordinates could be reduced to values
smaller than 7
which is the standard systematic error of ROSAT
observations.
For different source classes like SSS, X-ray binary, SNR, Galactic stars, and background AGN classification criteria could be derived from the extent and hardness ratios of the identified sources. We looked for flux variability of the sources and for likely optical counterparts. Five newly detected HRI sources were classified as candidates for SNRs because of their extent, two HRI sources which were identified with an LMC O and a B star as HMXB candidates. Eleven sources with probable bright optical counterpart and small X-ray to optical flux ratio are classified as stellar sources. Three sources with hard and/or absorbed X-ray spectrum indicated by the PSPC hardness ratios are likely candidates for X-ray binaries or AGN. Two of the hard X-ray sources show flux variability and for each of these an optical counterpart was found.
With the help of HRI observations many new X-ray sources were found. Further follow-up observations in X-ray, optical, or radio wavelengths with spectral information are needed to characterize these sources in more detail.
Acknowledgements
The ROSAT project is supported by the German Bundesministerium für Bildung und Forschung (BMBF) and the Max-Planck-Gesellschaft. This research has been carried out by making extensive use of the SIMBAD data base operated at CDS, Strasbourg, France.
Copyright The European Southern Observatory (ESO)