arXiv subjects

F. Haberl

Publications and source records attributed to F. Haberl.

256 records · Page 15Linked to original sources

arXiv1997

Identification of selected sources from the ROSAT Galactic Plane Survey - I

We report on optical searches in the error circles of 93 ROSAT survey sources located at low galactic latitudes (|b| < 20 deg). These sources were extracted from the ROSAT Galactic Plane Survey using various selection criteria on hardness ratio, X-ray and optical brightness and integrated galactic absorption in the direction of the source. We find optical identifications in 76 cases, among which are 25 new AGN, 6 new CVs and a new Be/X-ray binary. In order to illustrate the relevance of the source selections applied here, we cross-correlated the ROSAT all-sky survey bright source list with SIMBAD. Different classes of X-ray emitters populate distinct regions of a multi dimensional parameter space involving flux ratios, galactic latitude and Nh. This relatively good segregation offers the possibility to build source samples with enhanced probability of identification with a given class. Complete optical identification of such subsamples could eventually be used to compute meaningful probabilities of identification for all sources using as basis a restricted set of multi-wavelength information.

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arXiv1997

X-ray observations of the slowest known Be/X-ray pulsars RX J0146.9+6121 and X Persei

We present ASCA and ROSAT observations of the Be/X-ray binary pulsars RX J0146.9+6121 and X Persei between 1990 and 1996. Measuring the neutron star spin period and X-ray luminosity of X Persei shows that the episode of low X-ray luminosity and monotonic spin-down since 1978 continued to at least August 1995. ASCA and ROSAT HRI observations of RX J0146.9+6121 detected the pulsar with the longest known neutron star spin period at low luminosities after the X-ray outburst seen by EXOSAT in August 1984. The large spin period decrease seen between 1984 and 1993 has nearly stopped at a period of 1407.3 s in February 1996. We discuss that the X-ray outburst behaviour of X Persei with respect to its Be star phase changes observed in the optical can be caused by an asymmetry in the matter distribution around the Be star.

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arXiv1996

New massive X-ray binary candidates from the ROSAT Galactic Plane Survey I - Results from a cross-correlation with OB star catalogues

We report the discovery of several new OB/X-ray accreting binary candidates. These massive systems were found by cross-correlating in position SIMBAD OB star catalogues with the part of the ROSAT all-sky survey located at low galactic latitudes (|b| < 20d) and selecting the early type stars which apparently displayed the most significant excess of X-ray emission over the `normal' stellar level. The present search is restricted to stars earlier than B6 and X-ray luminosities > 10^31 erg/s. Follow-up optical and X-ray observations allowed to remove misidentified OB stars and spurious matches with interloper X-ray emitters (mostly active coronae) leaving five very likely new massive X-ray binaries. These new candidates have 0.1-2.4 keV un-absorbed luminosities > 10^33 erg/s indicating an accreting neutron star or black hole. On the average their soft X-ray luminosities are comparable to those observed from hard X-ray transients in quiescence or from persistent low luminosity Be/X-ray sources. Two additional X-ray binary candidates require further confirmation of their X-ray excess. Their lower soft X-ray luminosities (1-5 10^32 erg/s) could qualify them as Be + accreting white dwarf systems.

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arXiv1996

The ROSAT Galactic Plane Survey: analysis of a low latitude sample area in Cygnus

We present the analysis of the point source content of a low galactic latitude region selected from the ROSAT all-sky survey. The test field is centered at l = 90deg, b = 0deg and has an area of 64.5 deg2. A total of 128 soft X-ray sources are detected above a maximum likelihood of 8. Catalogue searches and optical follow-up observations show that in this direction of the galactic plane, 85% of the sources brighter than 0.03 PSPC cts/s are identified with active coronae. F-K type stars represent 67% (+/-13%) of the stellar identifications and M type stars account for 19% (+/- 6%). These results together with those of similar optical campaigns demonstrate that the soft X-ray population of the Milky Way is largely dominated by active stars. The modelling of this population suggests that most of the stars detected by ROSAT in this direction are younger than 1 Gyr. The small number of unidentified sources at low X-ray flux put rather strong constraints on the hypothetical X-ray emission from old neutron stars accreting from the interstellar medium. Our observations clearly rule out models which assume no dynamical heating for this population and a total number of Nns = 10^9 neutron stars in the Galaxy. If accretion on polar caps is the dominant mode then our upper limit may imply Nns ~ 10^8.

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