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The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| The ROSAT Bright Survey: I. Identification of an AGN sample with hard ROSAT X-ray spectra.
The ROSAT Bright Survey (RBS) aims to completely optically identify themore than 2000 brightest sources detected in the ROSAT all-sky survey atgalactic latitudes |b| > 30 degr (excluding LMC, SMC, Virgo cluster).This paper presents a subsample of 66 bright point-like ROSAT surveysources with almost hard PSPC spectra, the hardness ratio HR1 is >0.5 for most of the sources. The subsample could be nearly completelyidentified by low-resolution optical spectroscopy with the followingbreakdown into object classes: 31 Seyfert galaxies, 22 BL Laccandidates, 5 clusters of galaxies 1 cataclysmic variable, and 5 brightstars. Only one object remained unidentified and one X-ray source was aspurious detect ion. The redshift distribution peaks around 0.06 for theSeyferts and around 0.13 for the BL Lac candidates. Observations withmedium spectral resolution were obtained for most of the new S eyfertgalaxies. A large fraction (20 objects) are type 1 Seyfert galaxies, theother fraction includes Seyfert galaxies of type 1.5 - 1.8 (5 objects),two LINERs, and 4 possible narrow-line Seyfert 1 galaxies (NLS1). Aboutone third of the new Seyfert's have nearby companion galaxies displayingeither emission or absorption lines at the same redshift. Among them area couple of systems showing direct morphological evidence forinteraction. The large fraction of interacting galaxies among our samplesuggests a scenario where interaction is the main trigger of AGNactivity.
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