- 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).
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/356/445
- Title:
- ROSAT-FIRST AGN correlation
- Short Name:
- J/A+A/356/445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a correlation of the ROSAT All-Sky Survey with the April 1997 release of the VLA 20cm FIRST (Cat. <VIII/59>) catalogue. We focus our analysis on the 843 X-ray sources which have unique radio counterparts. The majority of these objects (84%) have optical counterparts on the POSS 1 plates. Approximately 30% have been previously classified and we obtain new spectroscopic classifications for 85 sources by comparison with the ongoing FIRST Bright Quasar Survey and 106 additional sources from our own new spectroscopic data. Approximately 51% of the sources are presently classified, and the majority of the unclassified objects are optically faint. The newly classified sources are generally radio weak, exhibiting properties intermediate with previous samples of radio- and X-ray-selected AGN. This also holds for the subsample of 71 BL Lacs which includes many intermediate objects. The 146 quasars show no evidence for a bimodal distribution in their radio-loudness parameter, indicating that the supposed division between radio-quiet and radio-loud AGN may not be real. The X-ray and radio luminosities are correlated over two decades in radio luminosity, spanning the radio-loud and radio-quiet regimes, with radio-quiet quasars showing a linear correlation between the two luminosities. Many of the sources show peculiar or unusual properties which call for more detailed follow-up observations. We also give the X-ray and radio data for the 518 X-ray sources for which more than one radio object is found. Because of the difficulties inherent in identifying optical counterparts to these complex sources, we do not consider these data in the current analysis.
- 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/143/391
- Title:
- ROSAT HRI catalogue of LMC X-ray sources
- Short Name:
- J/A+AS/143/391
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ROSAT HRI LMC source catalogue is based on all 543 pointed observations of the ROSAT HRI between 1990 and 1998 with exposure times higher than 50 sec. The observations covered a 10 deg x 10 deg field including the LMC. The catalogue contains 397 X-ray sources. Sources showing flux variability in ROSAT HRI and PSPC are listed in Table 1. Table 2 contains HRI sources which were identified with known objects in other catalogues and literature. Table 3 is a list of new classifications. The whole source catalogue from HRI observations is given in Table 4.
- 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/MNRAS/326/1161
- Title:
- ROSAT medium-sensitivity Galactic plane survey
- Short Name:
- J/MNRAS/326/1161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a moderately deep soft X-ray (0.1-2keV) survey of the Galactic plane using pointed observations with the ROSAT Position Sensitive Proportional Counter (PSPC). The survey is more than an order of magnitude more sensitive than previous X-ray surveys near the Galactic plane. The data consist of nine fields each of ~10ks exposure, pointed at positions on or very close to the Galactic plane (|b|<0.3{deg}) in the longitude range 180{deg}<~l<~280{deg}. This region has relatively low X-ray absorbing material out to distances of several hundred pc and presents fewer source-confusion problems than at other longitudes. The total sky area surveyed was 2.5deg^2^ this yielded 93 sources, 89 of which were detected in the hard (0.4-2.0keV) band. Nine sources were detected in both soft (0.1-0.4keV) and hard bands. In the hard band, the survey coverage is 90 per cent for sources brighter than 0.002count/s (~2x10^-14^erg/cm^2^/s), but falls steeply below this value, with the weakest sources being ~0.001count/s. The median limiting flux is <~0.0013count/s (~1.3x10^14^erg/cm^2^/s). There are 64 sources with hard-band count rates >0.002count/s. We present the catalogue of X-ray sources and the number-flux relations (logN-logS). Eighteen sources have possible identifications from the SIMBAD data base. We have searched the Tycho-2 (Cat. <I/259>) and USNO-A2.0 (Cat. <I/252>) catalogues to find all possible optical counterparts brighter than 19th magnitude, and attempt to classify these on the basis of log(FX/Fopt) versus optical colour diagrams and near-infrared photometry from the 2MASS Second Incremental Data Release (Cat. <B/2mass>). Hence, we have found the majority of these sources to be consistent with being late-type main-sequence stars, as previous studies have proposed from incompletely identified surveys. Comparison of the measured number-flux relations with predictions of Galactic (stellar) and extragalactic populations supports the view that the population of young stars in the plane is denser than previously thought.
- ID:
- ivo://CDS.VizieR/J/ApJS/162/304
- Title:
- ROSAT NEP X-ray source catalog
- Short Name:
- J/ApJS/162/304
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The sky around the North Ecliptic Pole (NEP), at 18:00:00+66:33:39, has the deepest exposure of the entire ROSAT All-Sky Survey (RASS, Cat. <IX/10>). The NEP is an undistinguished region of moderate Galactic latitude, b=29.8{deg}, and hence suitable for compiling statistical samples of both Galactic and extragalactic objects. We have made such a compilation in the 80.6{deg}^2^ region surrounding the NEP. Our sample fully exploits the properties of the RASS, since the only criteria for inclusion are source position and significance, and it yields the deepest large solid angle contiguous sample of X-ray sources to date. We find 442 unique sources above a flux limit ~2x10^-14^ergs/cm^2^/s in the 0.5-2.0keV band. In this paper we present the X-ray properties of these sources as determined from the RASS. These include positions, fluxes, spectral information in the form of hardness ratios, and angular sizes. Since we have performed a comprehensive optical identification program we also present the average X-ray properties of classes of objects typical of the X-ray sky at these flux levels. We discuss the use of the RASS to find clusters of galaxies based on their X-ray properties alone.