Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Galaxy clusters”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Ultraviolet background radiation.

The results are reported of observations in narrow bands centered on 1115, 1425, and 1446 A of the flux from an empty high-galactic-latitude region and from several stars. The observations had been obtained with the aid of three ultraviolet-sensitive Geiger counters which were carried on an Aerobee-150 rocket launched from the White Sands missile range on Mar. 13, 1969. The results obtained provide a basis for setting an upper limit to the flux from the Coma cluster of galaxies.

Henry, R. C.↗
NASA NTRS1974

Observation of soft X-rays from extended sources

Efforts were directed toward surveying several supernova remnants for the emission of soft X-rays. Rather than attempt to detect such faint X-ray emission, the program was redirected to observe the spectrum and angular structure of the extended X-ray source in the Perseus cluster of galaxies and the super-nova remnant Puppis A. An attempt was made to detect X-ray line emission from Puppis A with a Bragg crystal spectrometer. Observations provide evidence for the presence of X-ray line emission in the spectrum of Puppis A near .65 keV.

Catura, R. C.↗
NASA NTRS1974

X-ray morphology of the Perseus cluster

A measurement of the spatial distribution of the X-ray flux from the Perseus cluster of galaxies is reported. The measurement was made with a one-dimensional X-ray telescope carried by an Aerobee sounding rocket on February 8, 1974. The results are compared with previous X-ray observations and optical measurements of the galaxy distribution. The data show the presence of a luminous feature centered on NGC 1275, considerable emission from extended regions, and a marked asymmetry between the E-W and N-S distributions in the X-ray flux.

Wolff, R. S.↗
NASA NTRS1975

X-ray astronomy in the Uhuru epoch and beyond /Newton Lacy Pierce Prize Lecture/

A review of results from the Uhuru satellite is presented. An intensive treatment of two subjects is given, rather than a broad review. First, Cyg X-1, a stellar X-ray source and a candidate for a black hole, is discussed; second, the X-ray source in the Perseus cluster of galaxies, which may be a cloud of hot intergalactic gas, is treated. In both cases, the train of logic used in establishing the nature of these objects is presented and evaluated. For both, while alternative explanations cannot be completely eliminated, they become more difficult to sustain when examined in detail, suggesting that the candidate explanations are more likely correct.

Kellogg, E. M.↗
NASA NTRS1975

Observation of soft X-rays from cosmic sources

A binary X-ray source, an extended extragalactic X-ray source and several nearby stars were surveyed for X-ray emission. The energy spectrum and time structure of X-ray flux from the binary source, Her X-l, was investigated in the range from 0.15 to 6 KeV. This source was observed at a binary phase of 0.18 with the system near elongation normal to the line of sight. Intense pulsations were observed in optical emission lines near this binary phase. The spectrum and angular distribution of X-ray emission from the X-ray source in the Virgo Cluster of Galaxies, near M 87, was also observed. In addition, the stars Alpha Leo, Zeta Her, and Epsilon Vir were investigated. Epsilon Aur and Alpha Aur were also scanned. These stars were studied since there is increasing evidence that such objects may be transient sources of soft X-rays.

Catura, R. C.↗
NASA NTRS1976

An ultrasoft X-ray source in Coma Berenices

An intense soft X-ray source with an extraordinary spectrum has been observed in Coma Berenices, 4 deg northeast of and not associated with the Coma cluster of galaxies. Two spectra, obtained at different times in a sounding-rocket flight, indicate that the source temperature in thermal models is less than 1 million K; a power-law model requires photon power-law indices steeper than n = -3. The intensity in the 44-165 A band is of the order of 5 by 10 to the -10th power erg/sq cm/sec, but no flux is present at energies 0.3-2.1 keV to a limit of 1 by 10 to the -10th power erg/sq cm/sec. The lack of bright stars or a supernova remnant in the error box implies that this may be a new class of soft X-ray sources.

Margon, B.↗
NASA NTRS1975

The SAS-3 X-ray observatory

The experiment section of the Small Astronomy Satellite-3 (SAS-3) launched in May 1975 is an X-ray observatory intended to determine the location of bright X-ray sources to an accuracy of 15 arc-seconds; to study a selected set of sources over a wide energy range, from 0.1 to 55 keV, while performing very specific measurements of the spectra and time variability of known X-ray sources; and to monitor the sky continuously for X-ray novae, flares, and unexpected phenomena. The improvements in SAS-3 spacecraft include a clock accurate to 1 part in 10 billion, rotatable solar panels, a programmable data format, and improved nutation damper, a delayed command system, improved magnetic trim and azimuth control systems. These improvements enable SAS-3 to perform three-axis stabilized observations of any point on the celestial sphere at any time of the year. The description of the experiment section and the SAS-3 operation is followed by a synopsis of scientific results obtained from the observations of X-ray sources, such as Vela X-1 (supposed to be an accreting neutron star), a transient source of hard X-ray (less than 36 min in duration) detected by SAS-3, the Crab Nebula pulsar, the Perseus cluster of galaxies, and the Vela supernova remnant.

Mayer, W. F.↗
NASA NTRS1977

X-ray signatures: New time scales and spectral features

The millisecond bursts from Cyg X-1 are investigated and the overall chaotic variability for the bulk of the Cyg X-1 emission is compared to that of Sco X-1, showing that the essential character is remarkably similar (i.e. shot noise) although the fundamental time scales involved differ widely, from a fraction of a second (for Cyg X-1) to a fraction of a day (for Sco X-1). Recent OSO-8 observations of spectra features attributable to iron are reviewed. In particular, line emission is discussed within the context of a model for thermal radiation by a hot evolved gas in systems as different as supernova remnants and clusters of galaxies. Newly observed spectral structure in the emission from the X-ray pulsar Her X-1 is reported.

Boldt, E. A.↗
NASA NTRS1977

A spectroscopic study of selected quasars with absorption redshifts greater than emission redshifts

Spectroscopic data are presented for seven quasars having absorption systems whose redshift is greater than that of emission lines. The objects examined include PKS 1229-02, 3C 298, 3C 205, B194, PHL 1222, 0736-06, and PKS 0119-04. The redshift systems of each quasar are described in detail, the empirical distribution of the relative numbers of absorption systems vs. emission-absorption redshift difference is determined, and errors in this distribution due to selection of the sample and to the incompleteness and inhomogeneity of the data are discussed qualitatively. Six groups of possibilities are considered for the origin of absorption systems with redshifts higher than the emission redshifts. It is concluded that two separate mechanisms must be invoked: intervening clouds bound in a cluster of galaxies where the quasar is embedded (for systems with an absolute relative velocity not exceeding about 3000 km/s) and gravitational acceleration of material ejected by the quasar (for systems with a relative velocity of at least 3000 km/s).

Weymann, R. J.↗
NASA NTRS1977

The evaporation of spherical clouds in a hot gas. II - Effects of radiation

The effects of radiation on the evaporation of spherical clouds in a hot medium are considered. The critical cloud radius at which radiative losses balance conductive heating is determined as a function of the external temperature and density. Smaller clouds evaporate, and larger clouds condense. The conditions under which the surfaces of the clouds may be detected are discussed. Net radiative losses for evaporating clouds are calculated, and an effective cooling function for a cloudy medium is obtained. The results may be applied to clouds in supernova remnants, in the interstellar medium, and in clusters of galaxies.

Mckee, C. F.↗
NASA NTRS1977

The correlation function for density perturbations in an expanding universe. II - Nonlinear theory

A formalism is developed to find the two-point and higher-order correlation functions for a given distribution of sizes and shapes of perturbations which are randomly placed in three-dimensional space. The perturbations are described by two parameters such as central density and size, and the two-point correlation function is explicitly related to the luminosity function of groups and clusters of galaxies

Mcclelland, J.↗
NASA NTRS1978

Compact and diffuse X-ray sources in the core of the Perseus cluster /Abell 426/

Data on the X-ray structure of the Perseus cluster of galaxies in the energy range from 2 to 10 keV are analyzed which were obtained during a 12-day observation with the rotating modulation collimator aboard SAS 3. In particular, the nature of the compact X-ray source coincident with NGC 1275 is examined. The data are shown to confirm the presence of a diffuse region of X-ray emission surrounding the nucleus of NGC 1275; it is found that a model which also includes a point source at the nucleus is consistent with the data if the point contribution is no larger than 20% of the X-ray flux detected within 3 to 5 arcmin of the galaxy. The results suggest that NGC 1275 may have accreted a large amount of gas from the intracluster medium and that the flux from the possible point source is consistent with a synchro/Compton model.

Helmken, H.↗
NASA NTRS1978

Location of unidentified weak X-ray sources by the HEAO-1 scanning modulation collimator

Four weak sources for which precise positions have been obtained from the HEAO-1 Scanning Modulation Collimator (MC) experiment are discussed. One source (4U 0446+44) with the center of the cluster of galaxies containing 3C129 and 3C129.1 has been identified, and its angular size has been measured. One source with a galactic star is identified, although it is at galactic latitude b = 51 deg. The other two sources, 2A 0526-328 and 2A 0922-317, remain unidentified.

Schwartz, D. A.↗
NASA NTRS1979

Fluctuations in microwave background radiation due to secondary ionization of the intergalactic gas in the universe

Secondary heating and ionization of the intergalactic gas at redshifts z approximately 10-30 could lead to the large optical depth of the Universe for Thomson scattering and could smooth the primordial fluctuations formed at z approximately 1500. It is shown that the gas motions connected with the large scale density perturbations at z approximately 10-15 must lead to the generation of secondary fluctuations of microwave background. The contribution of the rich clusters of galaxies and young galaxies to the fluctuations of microwave background is also estimated.

Sunyayev, R. A.↗
NASA NTRS1978

Si XIII and Si XIV line emission search with the ANS crystal spectrometer

The final results of the search for Si XIII and Si XIV line emission, using the ANS Bragg crystal spectrometer, are presented. No positive line detection was achieved in any of the measurements made on several types of cosmic object; i.e., a transient X-ray source, close binary systems, supernova remnants, GX sources, and clusters of galaxies. Three-sigma upper limits for discrete line emission from these objects are reported and compared with line strengths inferred from other proportional-counter and Bragg spectrometer data. The present upper limit of 1.0 eV for the equivalent width of a narrow Si XIV line emission from the X-ray nova A0620-00 is an order of magnitude lower than previous limits set by other experiments.

Parsignault, D. R.↗
NASA NTRS1979

HEAO A-2 extragalactic results

Results from the HEAO A-2 experiment concerning the extragalactic X-ray sky are discussed. All-sky maps of hard X-ray sources detected are presented reflecting the temporal variability of the sources that make up the extragalactic X-ray sky. Most of the identified extragalactic objects are not clusters of galaxies but isolated galaxies. Spectra for sources representing classes of active galz galaxies, BL Lacertae objects, and N galaxies are discussed in order of luminosity.

Boldt, E. A.↗
NASA NTRS1979

A-3 scientific results - extragalactic

The results of the HEAO A-3 experiment are summarized. Specific contributions of the experiment to extragalactic astronomy are emphasized. The discovery of relatively condensed X-ray emission in the cores of those clusters of galaxies which are dominated by a giant elliptical or cD galaxy, the discovery of extended X-ray emitting plasma in groups of galaxies, and the demonstration that BL Lac objects are a class of X-ray sources are among the topics discussed.

Schwartz, D. A.↗
NASA NTRS1979

The Spacelab Wide Angle Telescope (SWAT)

A fast wide angle telescope that will be capable of imaging to the darker sky limit and in the ultraviolet wavelength region available above the atmosphere is described. The telescope (SWAT) has a resolution comparable to that of the large ground-based Schmidt telescope and a field of at least five degrees. A number of astrophysically important investigations can only be accomplished with such a telescope, e.g., detection of hidden, hot objects like hot white dwarfs and subwarfs in stellar binary systems, and energetic regions in globular clusters and galaxy nuclei. It permits unique studies of the UV-morphology of extended objects and allows discovery of very faint extensions, halos, jets, and filaments in galaxies. It can contribute to the investigation of dust in the Milky Way and in other galaxies and, with an objective prism, spectra of very faint objects can be obtained. The SWAT will localize objects for further study with the narrow-field Space Telescope.

West, R. M.↗