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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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NASA NTRS1979

A limit to the X-ray luminosity of nearby normal galaxies

Emission is studied at luminosities lower than those for which individual discrete sources can be studied. It is shown that normal galaxies do not appear to provide the numerous low luminosity X-ray sources which could make up the 2-60 keV diffuse background. Indeed, upper limits suggest luminosities comparable with, or a little less than, that of the galaxy. This is consistent with the fact that the average optical luminosity of the sample galaxies within approximately 20 Mpc is slightly lower than that of the galaxy. An upper limit of approximately 1% of the diffuse background from such sources is derived.

Worrall, D. M.↗
NASA NTRS1978

NGC 2110 - An X-ray/radio galaxy with elliptical morphology

The detection of X-ray emission from NGC 2110, a narrow-emission-line galaxy of apparently elliptical morphology, is reported. A relatively hard 2-11-keV energy spectrum with an index of 0.1 + or - 0.3 is obtained, and the X-ray luminosity in this energy band is shown to be 1.2 x 10 to the 43rd erg/s for the redshift distance of 43 Mpc. Optical and radio observations are discussed which indicate a galactocentric redshift of approximately 0.0071, a resolved nonstellar optical nucleus about 4 arcsec in extent, Seyfert type 2 emission lines from the nucleus, and a nonthermal radio source located 3.0 arcsec from the position of the optical nucleus. No evidence is found for X-ray source variability in NGC 2110. It is suggested that the four to seven known X-ray-emitting high-excitation narrow-emission-line galaxies appear to be nearby examples of the Seyfert type 2 phenomenon and that the elliptical morphology of NGC 2110, if confirmed, may be unique among known Seyfert galaxies.

Bradt, H. V.↗
NASA NTRS1979

Evidence for a massive X-ray halo around Markarian 541

Mkn 541, a Type I Seyfert galaxy, has been detected as an X-ray source with the rotating modulation collimator on SAS 3. The galaxy, which is identified as the optical counterpart of 4U 2351+06, has an X-ray flux of 3 x 10 to the -11th erg/sq cm per sec, which corresponds to a luminosity of 2 x 10 to the 44th erg/s at 240 Mpc. Evidence is presented that the X-rays are emitted in a volume of diameter 150 kpc. A variety of possible emission mechanisms are investigated, and it is suggested that the X-rays are caused by thermal bremsstrahlung from 500 billion solar masses of hot gas trapped in the gravitational well of Mkn 541, which implies that the mass of the galaxy exceeds 5 trillion solar masses. The hot gas can be explained as the accumulated ejecta of the Seyfert nucleus.

Cash, W.↗
NASA NTRS1979

3C 279 - The case for 'superluminal' expansion

The compact extragalactic radio source 3C 279 was observed with the Haystack-Goldstone interferometer (wavelength approximately 3.8 cm) during six separate sessions spread between October 1970 and April 1972. The fringe amplitudes from each of these observation sessions were consistent with a two-component model of the brightness distribution of the source. The position angle of the line joining the components remained at 38 + or - 2 deg, while the angular separation between the components increased nearly linearly at the rate of 0.5 + or 0.1 milliarcsec/yr during this period. The corresponding apparent expansion speed is (21 + or - 4)c, for H = 50 km/s per Mpc and q = 0.05

Cotton, W. D.↗
NASA NTRS1980

The HEAO A-2 survey of Abell clusters and the X-ray luminosity function

The HEAO A-2 all sky data base was surveyed for 2-10KeV X-rau emission from the 225 Abell clusters og galaxies listed in Abell's (1958) catalog which are of distance class four or less, and are within the fraction of the sky surveyed completely by Abell. Thirty-two identifications of clusters with X-ray sources were made, for which 2-10 KeV fluxes and 90% error boxes are presented. Twelve of these identification are new. The X-ray luminosity function was derived for this statistically complete sample and the best exponential fit was found to be f(L) = 20.2 x 10 to the minus 8 power exp (-l(44)/1.9) per cu Mpc 2-10KeV. The relationship between X-ray luminosity and richness was examined and a correlation was found for richness classes 0, 1, and 2. The relationship of X-rau luminosity, Bautz-Morgan type, and Rood-Sastry type was examined. It was found that BM type I's and RS type cD and B have the greatest average luminosity. The contribution of clusters to the X-ray background was calculated from the luminosity function and was found to be 5%, and with 90% certainty, less than 8% in the 2-10 KeV band pass.

Mckee, J. D.↗
NASA NTRS1979

A search for X-ray bursts from extragalactic supernovae using the HEAO 1 satellite

The soft X-ray data from the low energy detectors of the HEAO 1 A-2 experiment are surveyed in the 0.15-3.0 keV range to search for X-ray bursts (less than 1 hour) from extragalactic supernovae predicted by Klein and Chevalier. To within the operating sensitivity of 0.08 photons per sq cm/s no events were discovered from the first 8 months of operation. This is consistent with the theoretical prediction that the probability of finding one such event is small. The HEAO 2 satellite should be capable of detecting supernovae out to 2000 Mpc; these events are of cosmological interest.

Klein, R. I.↗
NASA NTRS1979

Detection of X-ray emission from distant clusters of galaxies

The paper reports the first extensive detection of X-ray emission from clusters of galaxies at cosmological distances. The properties of these objects are similar to those observed in objects at low redshifts. The 0.5-4.5 keV luminosities are in the range of less than 1 x 10 to the 43rd to 2 x 10 to the 45th ergs/s; the core radii are on the order of 0.5 Mpc; and Bautz-Morgan type I clusters are more luminous than types II or III. The observations are consistent with models assuming an evolving cluster potential and moderately efficient galaxy formation, but do not require them when observational selection is considered. X-ray observations of the 3C 295 cluster indicate that there is sufficient intergalactic medium to cause stripping of the cluster spirals, but the colors of these galaxies imply that they have not been stripped. A possible explanation of this discrepancy is discussed.

Henry, J. P.↗
NASA NTRS1980

X-ray quasars

Observational data for the seven quasars or Seyfert-quasar transition objects identified with X-ray sources is reviewed for radio, infrared, optical, ultraviolet, X-ray and gamma-ray frequencies. The observational histories of the quasars 3C 273, MR 2251-178 and 0241+622 and the quasar-like Seyfert nuclei Fairall-9, Mk 509, IC 4329A and IIIZw 2 are discussed in detail, and it is noted that their X-ray variability and spectra do not differentiate them from Seyfert nuclei, supporting the similarity between the several types of active extragalactic nuclei. The space density of the six objects (excluding 3C 273) within 600 Mpc is found to be comparable to that of other Seyferts and quasars, suggesting that X-ray emitting objects constitute a substantial fraction of the luminous transition objects in the neighborhood of the Galaxy. It is also pointed out that observations of the X-ray variability of these objects, which indicates that the X-rays originate from compact regions, represent a promising means for the further understanding of the emission process.

Bradt, H. V.↗
NASA NTRS1980

Distorted radio sources in Abell 2255 - Evidence of intergalactic gas 2.5 to 5 megaparsecs from the cluster center

Spectroscopic data are presented for radio galaxies in the A2255 region. The results indicate that the galaxies associated with distorted radio sources 2.5-5 Mpc projected radius from the cluster center are indeed cluster members. This implies the presence of substantial intergalactic gas 10-20 core radii from the cluster center. Reasonable assumptions concerning the gas distribution result in an estimated minimum mass for the A2255 intracluster gas of 4 x 10 to the 14th solar masses.

Hintzen, P.↗
NASA NTRS1980

QSO evolution and the intergalactic medium

A model is developed of a cold, photoionized intergalactic medium in which only discrete, evolving sources (quasars) produce the observed extragalactic hard X-ray background. Constraints on the model are imposed by observed optical depth limits to various redshifts, far UV and visible flux measurements, X-ray background and source counts in the region 2-6 keV, and it makes use of results of the Palomar Bright Quasar Survey and the Braccesi Quasar survey to obtain expressions for the quasar evolution function, absolute luminosity, present number density and switch-on redshift. Results of computer modeling reveal an intergalactic medium with a density with respect to closure less than 0.35, temperature of 16,000 K and fractional ion abundances of approximately 0.000001 for H I and 0.001 for He II, under the assumption of a Hubble constant of 50 km/sec per Mpc. In addition, spectral indices of -0.4 and -1.3 are obtained for the regions of the emission spectrum above and below 4 x 10 to the 18th Hz.

Sherman, R. D.↗
NASA NTRS1980

Closed loop performance of a brushless dc motor powered electromechanical actuator for flight control applications

A comprehensive digital model for the analysis and possible optimization of the closed loop dynamic (instantaneous) performance of a power conditioner fed, brushless dc motor powered, electromechanical actuator system (EMA) is presented. This model was developed for the simulation of the dynamic performance of an actual prototype EMA built for NASA-JSC as a possible alternative to hydraulic actuators for consideration in Space Shuttle Orbiter applications. Excellent correlation was achieved between numerical model simulation and experimental test results obtained from the actual hardware. These results include: various current and voltage waveforms in the machine-power conditioner (MPC) unit, flap position as well as other control loop variables in response to step commands of change of flap position. These results with consequent conclusions are detailed in the paper.

Demerdash, N. A.↗
NASA NTRS1981

Large-scale anisotropy of the cosmic microwave background radiation

Inhomogeneities in the large-scale distribution of matter inevitably lead to the generation of large-scale anisotropy in the cosmic background radiation. The dipole, quadrupole, and higher order fluctuations expected in an Einstein-de Sitter cosmological model have been computed. The dipole and quadrupole anisotropies are comparable to the measured values, and impose important constraints on the allowable spectrum of large-scale matter density fluctuations. A significant dipole anisotropy is generated by the matter distribution on scales greater than approximately 100 Mpc. The large-scale anisotropy is insensitive to the ionization history of the universe since decoupling, and cannot easily be reconciled with a galaxy formation theory that is based on primordial adiabatic density fluctuations.

Silk, J.↗
NASA NTRS1981

The Ophiuchus cluster - A bright X-ray cluster of galaxies at low galactic latitude

The discovery of an extended X-ray source identified with a cluster of galaxies at low galactic latitude is reported. The source, designated the Ophiuchus cluster, was detected near 4U 1708-23 with the HEAO 1 Scanning Modulation Collimator, and identified with the cluster on the basis of extended X-ray size and positional coincidence on the ESO/SRC (J) plate of the region. An X-ray flux density in the region 2-10 keV of approximately 25 microJ was measured, along with an X-ray luminosity of 1.6 x 10 to the 45th ergs/sec and an X-ray core radius of approximately 4 arcmin (0.2 Mpc) for an assumed isothermal sphere surface brightness distribution. The X-ray spectrum in the range 2-10 keV obtained with the HEAO 1 A-2 instrument is well fit by a thermal bremsstrahlung model with kT = 8 keV and a 6.7-keV iron line of equivalent width 450 eV. The steep-spectrum radio source MSH 17-203 also appears to be associated with the cluster, which is the closest and brightest representative of the class of X-ray clusters with a dominant central galaxy.

Johnston, M. D.↗
NASA NTRS1981

The dynamics of superclusters - Initial determination of the mass density of the universe at large scales

The radial velocities of cluster members of two rich, large superclusters have been measured in order to probe the supercluster mass densities, and simple evolutionary models have been computed to place limits upon the mass density within each supercluster. These superclusters represent true physical associations of size of about 100 Mpc seen presently at an early stage of evolution. One supercluster is weakly bound, the other probably barely bound, but possibly marginally unbound. Gravity has noticeably slowed the Hubble expansion of both superclusters. Galaxy surface-density counts and the density enhancement of Abell clusters within each supercluster were used to derive the ratio of mass densities of the superclusters to the mean field mass density. The results strongly exclude a closed universe.

Ford, H. C.↗
NASA NTRS1981

Einstein observations of the region between the Abell clusters of galaxies A401 and A399

Results of Einstein (HEAO 2) observations of the region between the Abell clusters A401 and A399 are presented. It is shown that each cluster has X-ray emission that extends about 2 Mpc from their respective centers. All of the emission between the two clusters can be explained as the simple superposition of foreground and background extended emission.

Ulmer, M. P.↗
NASA NTRS1981

The relation between velocity dispersion and central galaxy density in clusters of galaxies

A correlation between cluster velocity dispersion and average central galaxy density is reported. The correlation covers the range from rich clusters to small groups of galaxies, or, in terms of velocity dispersion, from v sub r approximately 1500 to approximately 100 km/s. This result is useful for estimating unknown velocity dispersions in clusters with the aid of the relatively easily determined 0.5 Mpc central galaxy density parameter. When combined with the virial theorem, the above relation also suggests that the mass-to-light ratio of galaxy systems increases with the system's velocity dispersion.

Bahcall, N. A.↗
NASA NTRS1981

One millimeter continuum observations of high redshift quasars

Upper limits to the one-millimeter continuum flux densities of the high redshift quasars B2 1225 + 31, Ton 490, and PHL 957 are presented. The upper limit to the power observed from these quasars at 1 mm is, on the average, one half of the observed power in the continuum at L-alpha. These observations are used to constrain the temperature of a hypothetical dust shell which reddens the quasar line and continuum emission by an extinction optical depth sufficient to account for the anomalously low L-alpha/H-alpha emission line ratio observed in each of these quasars. For the quasars studied, dust shell temperatures between 25 K and 50 to 95 K are prohibited by the present data. A dust shell at a temperature within this span reradiating all the power absorbed from the quasar ultraviolet continuum would produce a one-millimeter flux density greater than the measured upper limit. The average radius of the model dust shell cannot be between 70 kpc and 1 Mpc.

Ennis, D. J.↗
NASA NTRS1981

Intergalactic shells at large redshift

The intergalactic shells produced by galactic explosions at large redshift, whose interiors cool by inverse Compton scattering off the cosmic background radiation, have a characteristic angular size of about 1 arcmin at peak brightness. At z values lower than 2, the shells typically have a radius of 0.5 Mpc, a velocity of about 50 km/sec, a metal abundance of about 0.0001 of cosmic values, and strong radiation in H I(Lyman-alpha), He II 304 A, and the IR fine-structure lines of C II and Si II. The predicted extragalactic background emission from many shells, strongly peaked toward the UV, sets an upper limit to the number of exploding sources at z values of about 10. Shell absorption lines of H I, C II, Si II, and Fe II, which may be seen at more recent epochs in quasar spectra, may probe otherwise invisible explosions in the early universe.

Shull, J. M.↗