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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20
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NASA NTRS1980

X-rays from G74.9 + 1.2 - An elderly Crab Nebula

The supernova remnant G74.9 + 1.2, which resembles the Crab Nebula in many of its radio properties, has been detected in 0.15-3 keV X-rays with the Imaging Proportional Counter on the Einstein Observatory. The intrinsic luminosity of the object is about 100 times weaker than the Crab Nebula in this band. The X-ray morphology is centrally brightened (not a shell) with a total extent about 5 arcmin (17 pc). The nearby, intense, compact radio source 2013 + 370 is also probably detected as an extended X-ray source. It is argued that G74.9 + 1.2 represents an object similar to the Crab Nebula but of age 4000-7000 years. If this is the case, the period of the pulsar or neutron star (whose loss of rotational energy fuels the nebula) is predicted to be 0.1-0.2 s.

Wilson, A. S.↗
NASA NTRS1980

X-ray properties of quasars

The X-ray properties of 111 catalogued quasars have been examined with the imaging proportional counter on board the Einstein Observatory. Thirty-five of the objects, of redshift between 0.064 and 3.53, were detected as X-ray sources. The 0.5-4.5-keV X-ray properties of these quasars are correlated with their optical and radio continuum properties and with their redshifts and variability characteristics. The X-ray luminosity of quasars tends to be highest for those objects which are bright in the optical and radio regimes and which exhibit optically violent variability. These observations suggest that quasars should be divided into two classes on the basis of radio luminosities, spectra, evolution and underlying morphology and that quasars can make up a significant portion of the diffuse soft X-ray background only if the slope of the optical quasar log N-log S relation is steeper than 2 to m sub b of about 21.5.

Ku, W. H.-M.↗
NASA NTRS1980

X-ray observations of Seyfert galaxies with the Einstein Observatory

Thirty-seven Seyfert galaxies have been observed with the Imaging Proportional Counter on the Einstein Observatory. X-ray emission from 20 Seyfert 1 galaxies, three of which have been previously detected, and from four Seyfert 2 galaxies. Significant correlations are found between the 2 keV X-ray flux and the nonstellar continuum near 3.5 microns, the nonstellar B band continuum, and the H-beta line flux, and also between 0.5-4.5 keV X-ray luminosity and the zero intensity width of the H-beta emission line and the H-beta forbidden O III ratio. These correlations apply to both types of Seyfert galaxy, as well as the X-ray selected QSOs of Gindlay et al., suggesting that the same physical process operates in each one over a continuous range of intrinsic luminosity.

Kriss, G. A.↗
NASA NTRS1980

X-ray variability in active galaxy nuclei and quasars in less than one day

Data obtained from the Einstein Observatory demonstrating variations in X-ray emission from the nuclei of active galaxies and quasars on time scales of hours rather than previously observed days or years is presented. Light curves obtained from the Einstein imaging proportional counter for the Seyfert 1 galaxy NGC 6814 and from the High Resolution Imager for the quasars OX 169 and 3C 273 are illustrated, and variations by factors greater than two on time scales less than 20,000 sec for the first two objects and by a factor of 10% on a time scale over 50,000 sec for 3C 273 are pointed out. The measurements are also used to determine that thermal bremsstrahlung cannot be the cause of the intensity decay in OX 169, and that, in the absence of relativistic effects, the efficiency for energy release in the matter involved in the emission of 3C 273 is at least 0.1.

Elvis, M.↗
NASA NTRS1980

X-ray studies of quasars and active galaxies with the Einstein Observatory

Preliminary results of the first six months of an X-ray survey of active galaxies and quasars performed with the imaging proportional counter on board the Einstein Observatory are presented. Consideration is given to detections of Seyfert galaxies, N galaxies, BL Lac objects and quasars, and properties of selected representative objects are discussed in detail. The statistical properties, including class averages and correlation coefficients, of the various X-ray active galaxies are calculated in an attempt to determine the relation of X-ray properties to the similarities and differences between the various classes of galaxies. Evidence is obtained for a continuity of high-energy behavior among all active galaxies, and it is noted that they all exhibit flux variability, often on a short time scale. The soft X-ray emission can be explained in terms of the synchrotron self-Compton model, or alternatively by thermal emission from hot gas. A significant correlation is obtained between the X-ray and optical fluxes for all objects considered, indicating that optical quasar counts may be used to infer the contribution of quasars to the diffuse X-ray background.

Ku, W. H.-M.↗
NASA NTRS1980

X-ray studies of clusters of galaxies with the Einstein Observatory

The paper reports on cluster observations made by the Columbia Astrophysics Laboratory with the Einstein Observatory. A plot of the 0.2-3.0 keV X-ray luminosity of two dozen randomly selected sources against the Bautz-Morgan class reveals no apparent correlation between X-ray brightness and cluster morphological type. Observing a field containing the Butcher and Oemler cluster CL0024+1654 (z = 0.39), the satellite detected a weak source coincident with the cluster center. An IPC (imaging proportional counter) image of the Coma cluster, the nearest and best studied of Abell's rich clusters, shows a smooth X-ray emission rising to a flat central plateau in the vicinity of the giant ellipticals, NGC4874 and NGC4889. Although individual galaxies emerge above the diffuse flux near the edge of the field at the level of 0.1% of the cluster emission, the central 40 minutes contain no fluctuations on the scale of approximately one minute to the 1%-level.

Helfand, D. J.↗
NASA NTRS1980

Observations of supernova remnants in the Large Magellanic Cloud with the Einstein Observatory

Consideration is given to the Large Magellanic Cloud (LMC), noting that above 2 keV, the X-ray luminosity of the LMC is dominated by emission from 3-5 point sources similar to the bright sources near the center of our own Galaxy. The imaging proportional counter aboard the Einstein Observatory has been used to locate about 40 X-ray sources in the LMC. Supernova remnants observed in the LMC are presented, noting X-ray position, X-ray counting rate, and radio flux. For the six brightest sources, X-ray spectra have been analyzed to determine temperatures and intrinsic luminosity corrected for the interstellar absorption. These data are compared for parameters for the young galactic remnant of Tycho's supernova. Attention is given to the ratio of X-ray luminosity to radio luminosity, and the data are discussed within the framework of the standard blast-wave theory. The results of applying the model to recorded observations are numerically presented. In addition to providing a sample of objects for investigations of supernova remnants, the data are applicable to studies of galaxies of other morphological types and individual objects, such as N49.

Helfand, D. J.↗
NASA NTRS1980

Einstein observations of active galaxies

X-ray observations of Cen A (NGC 5128) and seven other X-ray emitting active galaxies are discussed which were made with the imaging proportional counter and the high-resolution imager aboard the Einstein Observatory. In addition to Cen A, the sources observed were the N-type galaxy 3C 120, the quasars OX 169 and 3C 273, and four Class 1 Seyfert galaxies, viz., Mkn 509, Mkn 79, NGC 6814, and NGC 4151. For Cen A, it is found that the X-ray data are dominated by a central point source of about 2 cts/sec, that X-ray elongations (possibly associated with the inner radio lobes) extend in the NE and SW directions, and that an X-ray jet exists which is aligned with the optical jet. The results for the other sources are used to derive emitting-region sizes and black-hole masses for models based on an accreting central black hole.

Tananbaum, H.↗
NASA NTRS1980

Einstein observations of quasars

X-ray observations of quasars with the imaging proportional counter and the high-resolution imager aboard the Einstein X-ray Observatory are reviewed. Detailed results are discussed for seven quasars with redshifts of 0.07 to 3.1. Data on 40 X-ray quasars observed with the Einstein imaging systems are summarized in the form of plots of 0.5-4.5-keV X-ray luminosity vs. redshift and of K-corrected X-ray emission vs. K-corrected optical flux. The results show that: (1) quasars as a class are luminous X-ray emitters; (2) quasars are a major contributor to the 2-keV X-ray background; (3) X-ray observations of quasars can be combined with observations of the X-ray background to set limits on the number of faint quasars; and (4) the Einstein imaging systems could detect quasars with redshifts of 3 to 10.

Tananbaum, H.↗
NASA NTRS1981

Einstein imaging observations of clusters with a bimodal mass distribution

Einstein imaging observations of four X-ray clusters of galaxies characterized by a double X-ray surface brightness and thus mass distribution are presented. The clusters A98, A115, A1750 and SC 0627-54 were found to exhibit two enhancements in their X-ray surface brightness distributions in observations made with the Einstein Imaging Proportional Counter. Calculations of the probability that the clusters represent chance superpositions indicate that the double clusters are physically associated. The radial distributions of the components are inconsistent with those of single point sources, and have been used to derive cluster luminosities which are typical of rich clusters. Masses of the subclusters are also found to be typical of bound and virialized clusters with gas contributing 10%. Within the framework of the hierarchical theory of galactic clustering, the double clusters are suggested to represent an intermediate evolutionary stage before the merger of subclusters into a relaxed Coma-type cluster.

Forman, W.↗
NASA NTRS1981

Nuclear Science Symposium, 27th, and Symposium on Nuclear Power Systems, 12th, Orlando, Fla., November 5-7, 1980, Proceedings

Advances in instrumentation for use in nuclear-science studies are described. Consideration is given to medical instrumentation, computerized fluoroscopy, environmental instrumentation, data acquisition techniques, semiconductor detectors, microchannel plates and photomultiplier tubes, reactor instrumentation, neutron detectors and proportional counters, and space instrumentation.

Martini, M.↗
NASA NTRS1981

The detection of X-ray variability in O stars

Seven O stars known to have strong, and sometimes variable, stellar winds have been observed repeatedly with the Imaging Proportional Counter on the Einstein Observatory, in a program designed to determine whether the X-ray fluxes from these stars are variable. In three cases, definite changes were seen, either on a time scale of a year (Iota Ori and Delta Ori) or five days (15 Mon). In two of these cases, the X-ray spectrum was harder when the overall flux was higher, indicating that some of the fluctuations may take place in a hot (approximately 10 to the 7th K) emitting region at the bottom of the winds.

Snow, T. P., Jr.↗
NASA NTRS1981

An X-ray survey of nine historical novae

The Einstein Observatory Imaging Proportional Counter has been used to search for X-ray emission from nine nearby historical novae. Six of the novae have been detected with estimated X-ray intensities between 0.1 and 4 keV of 10 to the -13th to 10 to the -11th erg/sq cm-sec, comparable to the intensities of previously detected cataclysmic variables. The X-ray intensity of one of the novae, V603 Aql, varies over times of several hundred seconds. The data suggest a correlation between the decay rate of the historical outburst and the current X-ray luminosity. Alternatively, the X-ray luminosity may be related to the inclination of the binary system.

Becker, R. H.↗
NASA NTRS1981

Simultaneous X-ray and optical observations of an Ursae Majoris during a low state

In November 1975, AN UMa was detected as a soft X-ray source with a 0.1-0.4 keV flux which was modulated with the orbital cycle. In order to investigate further this orbital dependence and to correlate it with existing photometric and spectroscopic observations to aid in determining the geometry of the system, simultaneous X-ray and optical observations were made throughout several cycles of AN UMa. The system was in a low optical state during the observations. The X-ray observations were made with the Imaging Proportional Counter on the Einstein Observatory, yielding measurements over an available energy range of 0.1-4 keV. Attention is given to total X-ray flux, the X-ray light curve, optical and infrared data, and model implications.

Szkody, P.↗
NASA NTRS1981

Direct observation of charge state abundances of energetic He, C, O, and Fe emitted in solar flares

The ionic charge states of helium, carbon, oxygen, and iron have been determined for three solar particle enhancements by an electrostatic deflection analyzer, which is combined with a thin window proportional counter dE/dX vs. E system. The observations are obtained during the periods September 23 to 29, 1978, June 6 to 8, 1979, and September 15 to 26, 1979, with an instrument onboard the ISEE-3 spacecraft. The mean ionic charge states for He, C, and oxygen exhibit a high degree of ionization with values of Q equals 2, 6, and 7.2, respectively. The charge state of iron is near 13 charge units. Variations from flare to flare and within the September 23, 1978 flare are small. The most surprising feature of the charge state measurement is the observation of a small (about 10%) but finite contribution of singly ionized helium.

Hovestadt, D.↗
NASA NTRS1981

Observations of the X-ray sources in the nearby Sc galaxy M33

Two observations of the Local Group spiral M33 with the Imaging Proportional Counter (IPC) on the Einstein Observatory reveal the presence of 11 point sources which, if at the distance of M33, have X-ray luminosities ranging from 10 to the 37th ergs/sec to 10 to the 39th ergs/sec. The brightest source, coincident with the nucleus of the galaxy, comprises approximately 70% of the total X-ray luminosity of the galaxy. If this source is a single source, it must be qualitatively different from the compact binary sources which dominate the X-ray luminosity of the Galaxy.

Long, K. S.↗
NASA NTRS1981

Imaging X-ray spectrophotometers

A new instrument which combines the good energy resolution of the gas scintillation proportional counter with the high position resolution of the microchannel plate is proposed. A study of the factors which determine the combined energy and position resolution of the new instrument is discussed. Submillimeter position resolution along with good energy resolution (8% fwhm at 6 keV) should be achievable.

Hailey, C. J.↗
NASA NTRS1981

Concurrent radio, infrared, optical and X-ray observations of the nucleus of the Seyfert galaxy NGC 4151

The nucleus of the Seyfert galaxy NGC 4151 was observed during May and June 1977 at X-ray energies from 20 to 200 keV using the high-energy X-ray spectrometer on OSO 8 at radio frequencies of 2695 and 8085. Data were also taken in the visual, and at infrared wavelengths of 1 to 2 microns, and from 2 to 6 keV using the OSO 8 proportional counter. Optical data showed variability by a factor of 2 within the observing period, which is comparable to the variability in the 2 to 6 keV X-ray flux. No variability, however, was measured at infrared or radio frequencies. The composite spectrum from radio to gamma-ray is plotted, and it is found that the optical and X-ray fluxes varied during the observing period, although it is not known if they varied concurrently.

Beall, J. H.↗