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  • Other Sources  (19)
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  • 1
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    The evolution of AGN's at x ray wavelengths (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The cosmological evolution and the Luminosity Function (LF) of x-ray selected Active Galactic Nuclei (AGN) are discussed. The sample used is extracted from the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) and consists of more than 420 objects. Preliminary results from the Rosat all sky survey data confirm the correctness of the optical identification of the EMSS sources, thus giving confidence to the results obtained from the analysis of the AGN sample. The XLF observed at different redshifts gives direct evidence of cosmological evolution. Data were analyzed within the framework of luminosity evolution models and the two most common evolutionary forms were considered. Luminosity dependent evolution is required if the evolution function has the exponential form, whereas the simpler pure luminosity evolution model is still acceptable if the evolution function has the power law form. Using the whole sample of objects the number counts and the devolved XLF were derived. A comparison of the EMSS Data with preliminary Rosat results indicates an overall agreement.
    Keywords: ASTROPHYSICS
    Type: MPI fuer Extraterrestrische Physik, X Ray Emission from Active Galactic Nuclei and the Cosmic X Ray Background; p 291-296
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  • 2
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    The Einstein Observatory extended medium sensitivity survey sample of BL Lacertae objects (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: We present new results on BL Lacertae Objects discovered in an extensive X-ray survey of the high galactic latitude sky performed by the Einstein satellite. While BL Lacs have been found primarily in high frequency radio surveys, we show that X-ray emission is an efficient new method for finding such objects and will offer an outstanding opportunity to find many of these objects in the near future using the ROSAT all-sky survey. It is also shown that X-ray selected BL Lac objects have somewhat different optical and radio properties than their radio selected counterparts. Using a complete, flux limited sample of 16 X-ray selected BL Lacs, we show that their number counts differ decisively from those of X-ray selected QSOs. Moreover, using the few red shifts available for these objects and limits on red shift determined from resolving the optical images of most of the remainder of the sample, a preliminary V/Vmax = 0.37 +/- 0.06. This value suggests an evolution in luminosity and/or density opposite in sense to that of QSOs.
    Keywords: ASTRONOMY
    Type: ; : TABES 93 - Annual
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  • 3
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    The Medium Sensitivity Survey and the X-ray selected quasar sample (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Statistical investigations of X-ray-emitting quasars are reviewed, focusing on the possible incompleteness of the Einstein IPC Medium Sensitivity Survey (MSS) (Maccacaro et al., 1982; Stocke et al., 1983; Gioia et al., 1984). The criteria used in constructing the MSS and calculating the source parameters are discussed, and the corrections determined for each line of sight by Maccacaro and Gioia (1986) on the basis of the H I measurements of Stark et al. (1986) are shown to have no effect on the completeness of the MSS extragalactic sample as a whole and of the quasar sample in particular. Other possible reasons for inconsistencies between the MSS sample and optically selected quasar samples are considered; ongoing efforts to expand the MSS sample are described; and some preliminary results are presented in graphs.
    Keywords: ASTROPHYSICS
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  • 4
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    BL Lacs from the EMSS: Number-counts and implications for the luminosity function (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: BL Lac objects, extracted from the Einstein Extended Medium Sensitivity Survey (EMSS), are examined. X-ray selection proved to be a powerful tool to find new BL Lacs, and allows the creation of complete, well defined and sizable samples. X-ray selected BL Lac objects (XBL) have in general more starlight in the optical spectra than radio selected BL Lacs. Redshifts for a significant fraction of objects in samples of XBL can be determined. It is thus possible to study the cosmological properties of BL Lac objects. Different models of luminosity functions of BL Lacs, including relativistic beaming, are considered and integrated over luminosity and redshift. The results are compared with the observed number-counts. The observed redshift distribution and the models' predictions are analyzed.
    Keywords: ASTRONOMY
    Type: ESA, The 23rd ESLAB Symposium on Two Topics in X Ray Astronomy. Volume 2: AGN and the X Ray Background; p 749-752
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  • 5
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    The properties of X-ray selected active galactic nuclei. II - A deeper look at the cosmological evolution (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A detailed study of the cosmological properties of X-ray selected AGN is presented. The data are analyzed within the framework of a pure luminosity evolution (PLE) model and the two most population evolutionary forms. Evidence is found for luminosity-dependent luminosity evolution if the evolution function has the exponential form. The simpler PLE model is more acceptable if the data are fitted with a power-law evolution function. Similar results are obtained in the optical domain from an analysis of a sample of optically selected QSOs with z less than 2.2 and B less than 20.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 389; 491-498
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  • 6
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    X-ray-selected candidates for the RS CVn and W UMa classes of binary stars (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: X-ray luminosity, spectral type, radial-velocity variation, rotationally broadened line profile, and Ca II H and K line emission data are used to identify 12 new candidates for the RS CVn class and seven new candidates for the W UMa class from spectroscopic binaries which are contained in the Einstein Extended Medium Sensitivity Survey. Under the assumption that the candidates are genuine members of each class, local space density estimates of 4.47 + or - 1.19 x 10 to the -4th/cu pc for RS CVn binaries and 8.47 + or - 3.00 x 10 to the -5th/cu pc for W UMa binaries are found. Although the density estimate for the W UMa binaries is shown to be consistent with previous estimates obtained from optically selected samples, the estimate for the RS CVn binaries is more than an order of magnitude greater than previously determined space densities.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 98; 692-698
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  • 7
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    The relation between X-ray emission and rotation in late-type stars from the perspective of X-ray selection (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: An X-ray-selected sample of 128 late-type (F-M) stars analyzed. These stars were identified as optical counterparts to serendipitous X-ray detections made by the Einstein Observatory Extended Medium Sensitivity Survey. Once identified as X-ray sources, the sample was followed up by an extensive program of optical observations, including high-resolution and low-resolution spectroscopy and photometry. Spectral types, luminosity classes, distances, X-ray luminosities, projected rotation rates (v sin i), radial velocities, and binary status have been determined for the sample.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 340; 1011-102
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  • 8
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    A cooling flow in a high-redshift, X-ray-selected cluster of galaxies (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The X-ray cluster of galaxies IE 0839.9 + 2938 was serendipitously discovered with the Einstein Observatory. CCD imaging at R and V wavelengths show that the color of the dominant elliptical galaxy of this cluster is significantly bluer than the colors of the next brightest cluster galaxies. Strong emission lines, typical of cD galaxies with cooling flows, are present in the spectrum of the dominant galaxy, from which a redshift of 0.193 is derived. The emitting line region is spatially resolved with an extension of about 13 kpc. All the collected data suggest that this cluster is one of the most distant cooling flow clusters known to date.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 104-110
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  • 9
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    ROSAT observations of four unidentified EMSS sources (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We present an analysis of four unidentified Einstein Observatory Extended Medium Sensitivity Survey sources detected in two pointed ROSAT/Position Sensitive Proportional Counter (PSPC) observations. One source (MS0420.0-3838) is resolved in two sources denoted with N (North) and S (South) in the ROSAT image. Only for one source (MS0420.6-3839) we have enough counts to allow a spectral analysis. For the other sources we have limited ourselves to the calculation of the x-ray hardness ratio and then, assuming a galactic value for the hydrogen column density, we have derived an energy index alpha (sub epsilon). We find a wide range of alpha(sub epsilon) (1 equal to or less than alpha(sub epsilon) equal to or less than 3). Thanks to a significantly improved x-ray positional accuracy, generally only one or two objects down to approx. 22 mag are present in the error circle. We have spectroscopically identified three sources with AGN: two are radio-quiet Quasi-Stellar Object (QSO) at z = 0.831 and z = 0.482, the third one is a Narrow Emission Line Galaxy at z = 0.572. For the remaining sources no optical spectroscopy is available; however, the values of alpha(sub ox) and alpha(sub ro) show that also these sources are probably AGN.
    Keywords: ASTRONOMY
    Type: The Astronomical Journal (ISSN 0004-6256); 108; 3; p. 970-977
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  • 10
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    X-ray surveys as tools to investigate the cosmological evolution of quasars, BL Lac objects and clusters of galaxies (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS) is presented. The MSS consists of X-ray sources serendipitously discovered with the IPC on board the Einstein Observatory in the energy range 0.3-3.5 keV, at fluxes between 10 to the -11th and 10 to the -13th ergs/sq cm/s. The basic properties of the extragalactic sources identified with AGN and clusters of galaxies are discussed.
    Keywords: ASTROPHYSICS
    Type: Observational cosmology; Aug 25, 1986 - Aug 30, 1986; Beijing; China
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