"The Unidentified X-ray Sources of the Hamburg/RASS Catalogue"
(November 1996 - October 1997)

Abstract

The question this thesis dealt with was: Which classes of X-ray emitters will be revealed from the unidentified X-ray sources of the Hamburg/RASS Catalogue? In order to find an answer to this question, further information about the possible optical counterparts listed in the catalogue was retrieved from the databases NED and SIMBAD, the radio surveys NVSS and FIRST, the optical survey POSS and the X-ray data registrated by ROSAT. The digitized photographic plates of the POSS served as a check for the positions of the optical candidates already determined by means of the Hamburg Schmidt plates. In addition, optical sources not visible on the Hamburg Schmidt plates inside the X-ray errror circle were searched for on these plates. From the radio surveys NVSS and FIRST information could be obtained about wether the optical candidates show any radio emission or not. The databases NED and SIMBAD yielded already known classifications of the optical candidates, whereas the ROSAT X-ray data provided further notion concerning the nature of the X-ray emitter. As a representative sample for the entire Hamburg/RASS Catalogue the unidentified X-ray sources with declinations within the ranges 0° to 10° and 35° to 45° were investigated. The resulting possible classification of these objects can be found in the catalogues in appendix A and B of this thesis. With the help of additional information, to be gathered as described above, the unidentified part of the Hamburg/RASS Catalogue can be reduced by a third. 23% of the investigated X-ray sources cold be classified as AGN, 7% as clusters of galaxies, 1% as galaxies and 2% as stars. Because of lack of information no classification could be proposed for the remaining 67%. Therefore a prognosis was elaborated for these X-ray sources using the results of this thesis and those of the identifica- tions carried out by Zickgraf et al. (1997) and Cordis et al. (1997). It follows that 75% of these sour- ces are expected to turn out as clusters of galaxies,whereas 25% should be confirmed as AGN. The complete identification of the Hamburg/RASS Catalogue is expected to yield the following distribution:

Furthermore the so called "empty fields" of the Hamburg/RASS Catalogue (X-ray sources without any optical counterpart on the Hamburg Schmidt plates inside a 40´´ error circle) were inves- tigated using the mentioned surveys and astronomical databases and the X-ray data delivered by ROSAT. The proposed classification for the empty fields can be found in the catalogue in appendix C of this thesis. 21% are expected to be AGN, 9% clusters of galaxies, 1% galaxies and 2% should turn out as variable stars. No possible classification could be obtained for 67% of the empty fields, but according to the prognosis elaborated within this thesis 60% of these should be confirmed as clusters of galaxies and 40% as AGN.