Engineering topics

Maccacaro, T.

Publications and source records attributed to Maccacaro, T..

45 records · Page 3

NASA NTRS1983

The Einstein observatory medium sensitivity survey - The quasars sample

A complete sample of X-ray-selected quasars and Seyfert galaxies extracted from the Einstein Observatory Medium Sensitivity Survey is described, and their physical characteristics are discussed. A Hubble constant of 50 km/s per Mpc and a Friedmann universe with a deceleration parameter of q(0)=0 are assumed throughout the survey, and the sample of X-ray sources was selected according to the following criteria: the significance of the detection exceeds a confidence level of 5 beta; the source is physically unrelated to the target of the IPC observation; and that the source is at a galactic latitude higher than 20 deg. The redshift and optical luminosity distributions of 55 Active Galactic Nuclei (AGNs) detected in the survey are discussed. A number flux relation for the different classes of extragalactic objects are analyzed in detail, using a Maximum Likelihood method and the assumption that the relation can be represented as a power law.

Gioia, I. M.↗

NASA NTRS1983

Luminosity function and cosmological evolution of X-ray selected quasars

The preliminary analysis of a complete sample of 55 X-ray sources is presented as part of the Medium Sensitivity Survey of the Einstein Observatory. A pure luminosity evolutionary law is derived in order to determine the uniform distribution of the sources and the rates of evolution for Active Galactic Nuclei (AGNs) observed by X-ray and optical techniques are compared. A nonparametric representation of the luminosity function is fitted to the observational data. On the basis of the reduced data, it is determined that: (1) AGNs evolve cosmologically; (2) less evolution is required to explain the X-ray data than the optical data; (3) the high-luminosity portion of the X-ray luminosity can be described by a power-law with a slope of gamma = 3.6; and (4) the X-ray luminosity function flattens at low luminosities. Some of the implications of the results for conventional theoretical models of the evolution of quasars and Seyfert galaxies are discussed.

Maccacaro, T.↗

NASA NTRS1982

Discovery of a new BL Lacertae object /1E 1402.3 + 0416/ with the Einstein Observatory

It is noted that only one BL Lac object, designated 1E 1402.3 + 0416, has so far been discovered as part of an optical identification program for a complete sample of faint X-ray sources detected with the Einstein Observatory. Consistent with previously X-ray-discovered BL Lacs, this object is blue and radio weak (17 mJy at 6 cm). It is pointed out that the percentage of BL Lacs in the faint extragalactic X-ray sample (2%) is smaller than the percentage at higher X-ray fluxes (6%). Over the same range in X-ray flux, the percentage of emission-line active galaxy nuclei (QSO + Seyferts) rises from 40% to 74%). This is seen as suggesting that BL Lacs do not evolve in a manner similar to quasars and are, therefore, not substantial contributors to the X-ray background.

Stocke, J.↗

NASA NTRS1982

X-ray observations with the Einstein Observatory of emission-line galaxies

X-ray observations of narrow-emission-line galaxies are presented and discussed. One source, NGC 1365, is found to be extended in the soft X-ray band; three others, NGC 2992, NGC 5506, and NGC 7582, have been observed to vary in intensity. The best fit spectral index and cutoff energy E sub a are derived for NGC 2992, NGC 5506, and NGC 7582. The X-ray spectra of these galaxies are similar to those of type 1 Seyfert galaxies. In the case of NGC 5506 and NGC 7582, the absorbing column N sub H derived is about one order of magnitude greater than predicted from the reddening of thy optical continuum and of the Balmer lines. Possible explanations for the discrepancy are discussed.

Maccacaro, T.↗

NASA NTRS1982

VLA observations of an unbiased sample of extragalactic X-ray sources

Results are presented of a Very Large Array survey at 6 cm of an unbiased sample of extragalactic X-ray sources serendipitously discovered with the Einstein X-ray Observatory. Fourteen of 42 X-ray sources are detected in the radio down to a limiting sensitivity of 1-2 mJy. Detections include eight of 31 examined active galactic nuclei (AGN-quasars or Seyferts), five of eight clusters of galaxies and one BL Lac object. The radio detection rate of X-ray selected AGNs is higher than that of optically selected AGNs, suggesting that a physical link between radio and X-ray emission is present. The radio properties of the X-ray selected clusters are similar to those of optically selected Abell clusters.

Feigelson, E. D.↗

NASA NTRS1982

Abell 2069 - An X-ray cluster of galaxies with multiple subcondensations

X-ray and optical observations of the cluster Abell 2069 are presented. The cluster is at a mean redshift of 0.116. The cluster shows multiple condensations in both the X-ray emission and in the galaxy surface density and, thus, does not appear to be relaxed. There is a close correspondence between the gas and galaxy distributions which indicates that the galaxies in this system do map the mass distribution, contrary to what might be expected if low-mass neutrinos dominate the cluster mass.

Gioia, I. M.↗

NASA NTRS1982

A medium sensitivity X-ray survey using the Einstein Observatory - The log N-log S relation for extragalactic X-ray sources

The paper presents results of an X-ray survey of about 50 sq deg of the high galactic latitude sky at sensitivities in the range of 7 x 10 to the -14 to 5 x 10 to the -12 ergs/sq cm/s. The number-flux relation is derived for the extragalactic population to yield a best-fit power-law slope of 1.53 + or - 0.16, and the content of the sample is analyzed in terms of types of sources, appearing to be significantly different from the content of similar samples selected at higher fluxes. The medium sensitivity sample of extragalactic sources is dominated by active galactic nuclei, while samples selected at higher fluxes and higher energies are dominated by clusters of galaxies. Thus, the number-flux relation for extragalactic sources may be interpreted to a first approximation as the sum of the two different distributions with flatter and steeper slopes describing clusters and AGNs, respectively.

Maccacaro, T.↗

NASA NTRS1982

Discovery of a narrow line quasar

A stellar object is reported which, while having X-ray and optical luminosities typical of quasars, has narrow permitted and forbidden emission lines over the observed spectral range. The narrow-line spectrum is high-excitation, the Balmer lines seem to be recombinational, and a redder optical spectrum than that of most quasars is exhibited, despite detection as a weak radio source. The object does not conform to the relationships between H-beta parameters and X-ray flux previously claimed for a large sample of the active galactic nuclei. Because reddish quasars with narrow lines, such as the object identified, may not be found by the standard techniques for the discovery of quasars, the object may be a prototype of a new class of quasars analogous to high-luminosity Seyfert type 2 galaxies. It is suggested that these objects cannot comprise more than 10% of all quasars.

Stocke, J.↗

NASA NTRS1981

X-ray studies of quasars with the Einstein Observatory. II

X-ray observations of 107 quasars have been carried out with the Einstein Observatory, and 79 have been detected. A correlation between optical emission and X-ray emission is found; and for radio-loud quasars, the data show a correlation between radio emission and X-ray emission. For a given optical luminosity, the average X-ray emission of radio-loud quasars is about three times higher than that of radio-quiet quasars. The data also suggest that the ratio of X-ray to optical luminosity is decreasing with increasing redshift and/or optical luminosity. The data support the picture in which luminosity evolution, rather than pure density evolution, describes the quasar behavior as a function of redshift.

Zamorani, G.↗