Stefan Dobereiner

Galaxy identifications in the ROSAT All-Sky Survey

In a correlation study of the ROSAT All-Sky Survey Bright Source Catalogue (RASS-BSC) with the Catalogue of Principal Galaxies (PGC) 904 X-ray sources were found that possess possible extragalactic counterparts within a search radius of 100 arcsec. A visual screening process was applied to classify the reliability of the correlations. 547 correlations have been quoted as reliable identifications. From these, 349 sources are known as active galaxies. Although for the other sources no hints for activity were found in the literature, 69% of those for which we have distances show X-ray luminosities exceeding those of normal galaxies, a clear sign that these galaxies also own hitherto unreported X-ray active components. Some objects are located inside or in the direction of a known group or cluster of galaxies. Their X-ray flux may therefore be in part affected by hot gas emission. Luminosity and

Broad-band X-ray observations of Cir X-1

\log N{-}\log S

HEXE observations 1991/1992

distributions are used to characterize different subsamples. Nuclei that are both optically and X-ray active are found predominantly in spirals. Two special source samples are defined, one with candidates for X-ray emission from hitherto unknown groups or clusters of galaxies, and one with high X-ray luminosity sources, that are likely candidates to possess hitherto unreported active galactic nuclei. Besides a compilation of X-ray and optical parameters, also X-ray overlays on optical images for all the objects are supplied as part of this work.

Black hole X‐ray novae and pair models

Abstract We present broad-band (2–88 keV) X-ray observations of the X-ray binary Cir X-1 with the TTM and HEXE instruments on board of the Mir space station. The observations were made in January/February 1989. The spectrum is best described by a model with 3 components: a blackbody at low energies, an iron line and a Comptonised hard continuum. The spectrum is variable during our observations; when the Comptonised component becomes harder, the spectrum becomes softer below 15 keV. The high-energy spectrum resembles that of X-ray binary pulsars.

The planet search program at the ESO Coudé Echelle spectrometer - III. The complete Long Camera survey results

We report observations with the HEXE instrument on the Kvant module aboard the Mir space station which were performed in late 1991 and 1992. We present results from the field containing MX 0836‐42 and GRS 0834‐430, and from the sources GX 5‐1, GRS 1758‐258, 1E 1740.7‐294. The most interesting observation is the first of these, since the high‐energy spectra of these two sources are not well known, contrary to those of the other objects reported here. We find a thermal spectrum with temperature ≊11 keV and no indication of a periodic signal. Since a power‐law type spectrum and pulsations have been observed from GRS 0834‐430, we believe that the source we observe is MX 0836‐42.

The ESO Precise RV Survey for Extra-solar Planets: Results from the First Five Years

X‐ray novae are among the best black hole candidates to date. Since galactic black holes are often regarded as ‘‘mini‐AGN’’, we test a simple pair and Compton reflection model, developed for AGN, with statistically more significant data of black hole X‐ray novae (BHXN) and Cyg X‐1 observed by the HEXE instrument. We find that we can fit the data with a model by Zdziarski (1993) and discuss the allowed parameter range.