- ID:
- ivo://CDS.VizieR/J/A+A/319/413
- Title:
- ROSAT detected quasars. I.
- Short Name:
- J/A+A/319/413
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled a sample of all quasars with measured radio emission from the Veron-Cetty - Veron catalogue (1993, VV93 <VII/166>) detected by ROSAT in the ALL-SKY SURVEY (RASS, Voges 1992), as targets of pointed observations, or as serendipitous sources from pointed observations as publicly available from the ROSAT point source catalogue (ROSAT-SRC, Voges et al. 1995). The total number of ROSAT detected radio quasars from the above three sources is 654 objects. 69 of the objects are classified as radio-quiet using the defining line at a radio-loudness of 1.0, and 10 objects have no classification. The 5GHz data are from the 87GB radio survey, the NED database, or from the Veron-Cetty - Veron catalogue. The power law indices and their errors are estimated from the two hardness ratios given by the SASS assuming Galactic absorption. The X-ray flux densities in the ROSAT band (0.1-2.4keV) are calculated from the count rates using the energy to counts conversion factor for power law spectra and Galactic absorption. For the photon index we use the value obtained for a individual source if the estimated 1 sigma error is smaller than 0.5, otherwise we use the mean value 2.14.
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- ID:
- ivo://CDS.VizieR/J/A+A/330/108
- Title:
- ROSAT detected quasars. II.
- Short Name:
- J/A+A/330/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled a sample of all radio-quiet quasars or quasars without radio detection from the Veron-Cetty - Veron catalogue (1993, VV93, Cat. <VII/166>) detected by ROSAT in the ALL-SKY SURVEY (RASS, Voges 1992, in Proc. of the ISY Conference `Space Science', ESA ISY-3, ESA Publications, p.9, See Cat. <IX/10>), as targets of pointed observations, or as serendipitous sources from pointed observations publicly available from the ROSAT point source catalogue (ROSAT-SRC, Voges et al. 1995, Cat. <IX/11>). For all sources we used the results of the Standard Analysis Software System (SASS, Voges et al. 1992, in Proc. of the ISY Conference `Space Science', ESA ISY-3, ESA Publications, p.223), employing the most recent processing for the Survey data (RASS-II, Voges et al. 1996, Cat. <IX/10>). The total number of quasars is 846. 69 of the radio-quiet objects with radio detections have already been presented in a previous paper (Brinkmann, Yuan, & Siebert 1997, Cat. <J/A+A/319/413>) using the RASS-I results. 17 objects were found to be radio-loud from recent radio surveys and were marked in the table. When available, the power law photon indices and the corresponding absorption column densities (NH) were estimated from the two hardness ratios given by the SASS, both with free fitted NH and for Galactic absorption. The unabsorbed X-ray flux densities in the ROSAT band (0.1-2.4keV) were calculated from the count rates using the energy to counts conversion factor for power law spectra and Galactic absorption. As the photon index we used the value obtained for the individual source if the estimated 1-{sigma} error is smaller than 0.5, otherwise we used the redshift-dependent mean value (see the paper for details).
- ID:
- ivo://CDS.VizieR/J/A+A/323/739
- Title:
- ROSAT detected quasars. II.
- Short Name:
- J/A+A/323/739
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the broad band, radio - to - X-ray, properties of a large sample of mostly previously optically unidentified radio-loud X-ray sources from the correlation of a ROSAT All-Sky Survey source list with the 5GHz Green Bank Survey of the northern sky (RGB sample) which is one of the largest well-defined flux-limited surveys of AGN ever obtained. Further, the RGB pushes 1-2 orders of magnitude deeper in both X-ray and radio flux compared to previous unbiased wide-area AGN surveys. Follow up VLA observations of the candidate objects yielded positions with arcsec accuracy which were used to find optical counterparts to the sources from digitized POSS plates. The sources are divided into three classes according to the positional offset between the X-ray and radio candidates and the spatial resolution of the radio observations, reflecting the various degrees of confidence about the correctness of the proposed association. Although the nature of the sources as well as their redshifts remain to be determined in spectroscopic follow up observations, the derived flux ratios lead to the conclusion that the majority of them are quasars. Hardly any correlations could be found between different source parameters, possibly due to the fact that most of the objects are found in a relatively small flux range near the sensitivity limit of the radio catalogue. The majority of the new RGB sources have broad-band properties between those of traditional radio-selected and X-ray selected AGN. There is no bimodal distribution in the radio-loudness distribution, and the traditional division between radio-quiet and radio-loud AGN may not be warranted.
- ID:
- ivo://CDS.VizieR/J/A+A/318/111
- Title:
- ROSAT Galactic Plane Survey
- Short Name:
- J/A+A/318/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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=90, b=0 and has an area of 64.5deg^2^. 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 0.03PSPC are identified with active coronae. F-K type stars represent 67% (+/-13%) of the stellar identifications and M type stars account for 19% (+/-6%). A small but significant number of X-ray sources are associated with A type stars on the basis of positional coincidence. 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. We show that the density and distribution in flux and spectral type of the active coronae detected in X-rays are consistent with the picture drawn from current stellar population models and age dependent X-ray luminosity functions. The modelling of this population suggests that most of the stars detected by ROSAT in this direction are younger than 1Gyr. This opens the possibility to extract in a novel way large samples of young stars from the ROSAT all-sky survey. 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 N_ns_=10^9^ neutron stars in the Galaxy. If accretion on polar caps is the dominant mode then our upper limit may imply N_ns_=~10^8^. Among the non coronal identifications are three white dwarfs, a Seyfert 1 active nucleus, two early type stars and one cataclysmic variable. We also report the discovery of a Me+WD close binary system with P_orb_=~12 .
- ID:
- ivo://CDS.VizieR/J/A+AS/132/341
- Title:
- ROSAT GPS optical identification
- Short Name:
- J/A+AS/132/341
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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 N_H_. 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.
- ID:
- ivo://CDS.VizieR/J/A+AS/147/75
- Title:
- ROSAT HRI catalogue of SMC X-ray sources
- Short Name:
- J/A+AS/147/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ROSAT HRI SMC source catalogue is based on all 71 pointed observations of the Small Magellanic Cloud by the ROSAT HRI between 1990 and 1998. The data was selected in a 5{deg}x5{deg} field covering the SMC. The catalogue which contains 121 X-ray sources, was cross-correlated with data bases and catalogues like SIMBAD, TYCHO, or USNO as well as other publications in order to classify the X-ray sources and find new candidates for various source classes.
- ID:
- ivo://CDS.VizieR/J/A+A/341/751
- Title:
- ROSAT HRI observations of the Pleiades
- Short Name:
- J/A+A/341/751
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a deep X-ray survey of the Pleiades open cluster, we use the ROSAT High Resolution Imager to explore a region of the cluster formerly surveyed with the PSPC. These new observations substantially improve upon both the sensitivity and the spatial resolution for this region of the Pleiades, allowing us to detect 18 cluster members not detected before and 16 members not included in the catalogs used in previous surveys. The high sensitivity of the present observations permits us to obtain more stringent upper limits for 72 additional members and also provides sufficient numbers of stars to enable us to explore the dependence of L_x_ on stellar rotation for the slow rotators of the Pleiades. Using the new high sensitivity X-ray observations and the recent rotational measurements we discuss the activity-rotation relationship in the Pleiades solar type stars. We also present new photometric observations of optical counterparts of a number of X-ray sources detected in previous surveys but not yet identified.
- ID:
- ivo://CDS.VizieR/IX/28A
- Title:
- ROSAT HRI Pointed Observations (1RXH)
- Short Name:
- IX/28A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The hricat.dat table contains a list of sources detected by the Standard Analysis Software System (SASS) in reprocessed, public High Resolution Imager (HRI) datasets. In addition to the parameters returned by SASS (like position, count rate, signal-to-noise, etc.) each source in the table has associated with it a set of source and sequence "flags". These flags are provided by the ROSAT data centers in the US, Germany and the UK to help the user of the ROSHRI database judge the reliability of a given source. These data have been screened by ROSAT data centers in the US, Germany, and the UK as a step in the production of the Rosat Results Archive (RRA). The RRA contains extracted source and associated products with an indication of reliability for the primary parameters.
- ID:
- ivo://CDS.VizieR/J/ApJ/519/533
- Title:
- ROSAT observations of ACO clusters
- Short Name:
- J/ApJ/519/533
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled an X-ray catalog of optically selected rich clusters of galaxies observed by the Position Sensitive Proportional Counter (PSPC) during the pointed GO phase of the ROSAT mission. This paper contains a systematic X-ray analysis of 150 clusters with an optical richness classification of R>=2 from the Abell, Corwin, & Olowin (1989; ACO) catalog. All clusters were observed within 45' of the optical axis of the telescope during pointed PSPC observations. For each cluster, we calculate: the net 0.5-2.0keV PSPC count rate (or 4{sigma} upper limit) in a 1Mpc radius aperture, 0.5-2.0keV flux and luminosity, bolometric luminosity, and X-ray centroid. The cluster sample is then used to examine correlations between the X-ray and optical properties of clusters, derive the X-ray luminosity function of clusters with different optical classifications, and obtain a quantitative estimate of contamination (i.e., the fraction of clusters with an optical richness significantly overestimated due to interloping galaxies) in the ACO catalog.
- ID:
- ivo://CDS.VizieR/J/A+A/311/384
- Title:
- ROSAT observations of BL Lacertae objects
- Short Name:
- J/A+A/311/384
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present soft X-ray spectra of 74 BL Lacertae objects observed with the PSPC detector on board of the ROSAT satellite. The sample contains all BL Lac objects detected during the pointed observation phase as a target or serendipitously. We have investigated the soft X-ray and broad band spectral properties and discuss the consequences for the X-ray emission processes. For the first time a clear dependence of the X-ray spectral steepness on the radio to X-ray spectral energy distribution is found: {alpha}_rx_ and {alpha}_x_ are correlated in the X-ray selected (XBL) subsample and anticorrelated in the radio selected (RBL) subsample. The objects with intermediate {alpha}_rx_ values thus do have the steepest soft X-ray spectra. Simulated PSPC spectra based on a set of simple two component multifrequency spectra are in good agreement with the measurements and suggest a broad range of synchrotron cutoff energies. We have calculated synchrotron self-Compton beaming factors for a subsample of radio bright objects and find a correlation of the beaming factors {delta}_IC_ with {alpha}_rx_ and {alpha}_x_. The most extreme RBL objects are very similar to flat spectrum radio quasars in all their broad band and X-ray properties.