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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 541 records · Page 30
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NASA NTRS1972

Techniques in balloon X-ray astronomy.

Since the first balloon observation of the Crab Nebula balloon data have provided much information on the positions, spectra, time variability and pulsed nature of localized sources, and on the spectrum and isotropy of diffuse galactic and universal components. Measurements are limited to energies above about 20 keV by atmospheric attenuation at 2 to 3 g/sq cm depth and to below several hundred keV by detector sensitivity. Detectors usually consist of large-area Na I or Cs I scintillation counters with anticoincidence collimators for rejection of charged particles and scattered X-rays. Proportional counters are occasionally used at lower energies and solid-state detectors are used where extreme energy resolution is important. The instruments require a pointing capability on the order of 1.0 to 0.1 deg, depending on the collimator aperture. Digital data is either recorded on board or telemetered using a PCM technique.

Peterson, L. E.↗
NASA NTRS1972

Cooling of dense stars

Cooling rates were calculated for neutron stars of about one solar mass and 10 km radius, with magnetic fields from zero to about 10 to the 14th power gauss, for extreme cases of maximum and zero superfluidity. The results show that most pulsars are so cold that thermal ionization of surface atoms would be negligible. Nucleon superfluidity and crystallization of heavy nuclei were treated quantitatively, and more realistic hadron star models were chosen. Cooling rates were calculated for a stable hyperon star near the maximum mass limit, a medium weight neutron star, and a light neutron star with neutron-rich heavy nuclei near the minimum mass limit. Results show that cooling rates are a sensitive function of density. The Crab and Vela pulsars are considered, as well as cooling of a massive white dwarf star.

Tsuruta, S.↗
NASA NTRS1973

The attenuation of X-rays emitted by supernovae

The attenuation of X-rays in Arnett's C-12 detonation supernova model is computed. The attenuation of X-rays in the filaments of the Crab Nebula is computed using a model for the filaments by Woltjer and a model by Davidson and Tucker. An empirical expression by Gorenstein, Kellogg, and Gursky for the optical thickness of the interstellar medium for three supernova remnants is analyzed.

Schocken, K.↗
NASA NTRS1973

Stellar X-ray polarimetry on OSO-1

The importance of stellar X-ray polarimetry is reviewed. A graphite crystal polarimeter sensitive near 2.6 and 5.2 keV which was designed for the OSO-1 satellite is described. The instrument's predicted performance for many stellar X-ray sources is presented, and the fundamental questions that can be resolved with the OSO-1 polarimeter are considered. The sensitivity of the instrument is such that, during an observation time of 24 hours, the polarization of the Crab nebula can be measured with an accuracy of 0.6 percent.

Landecker, P. B.↗
NASA NTRS1973

Recent Observations of Cosmic Gamma Rays from 10 Mev to 1 Gev

Recent observations of cosmic gamma-rays made subsequent to the discovery of energetic photons from the galactic plane are analyzed. Three main areas under current investigation are treated. They are: (1) gamma ray emission from the plane of the galaxy, with emphasis on observations made in the vicinity of the galactic center, (2) gamma ray emission from the Crab nebula and its pulsar, and (3) diffuse gamma radiation.

Share, G. H.↗
NASA NTRS1973

The magnetospheric structure of pulsars

A model of pulsar magnetospheres is described which has evolved inductively from the work of Sturrock, where the radiation is produced near the surface of a neutron star. Some of the theoretical ideas of others, particularly those of Sturrock, are discussed. The braking index n and period-pulse-width distribution of pulsars are first reinvestigated by relaxing the conventional assumption that R sub Y = R sub L, where R sub Y is the radius of the neutral points marking the transition from closed to open magnetic field lines, and R sub L is the radius of the light cylinder. This is replaced by the parameterization R sub Y = R sub * (1- eta )power R sub L (eta), where R sub * is the neutron star radius. If the ratio frequency radiation is created near the surface and beamed along open field lines, it is found that a good fit to the period-pulse-width distribution can be obtained for eta in the range 0.5 = or eta = or 0.7. The relation n = 1 + 2 eta then gives n = 2.2 + or - 0.2, which is in good agreement with the values measured for the Crab pulsar.

Roberts, D. H.↗
NASA NTRS1973

Hard cosmic X-ray sources.

A review of the observational status of X-ray sources detected in the 20 to 500 keV range is presented. Of the approximately 115 sources listed in the March 1972 edition of the UHURU 2-6 keV sky survey catalog, about 15 sources have been studied in hard X rays. Most of the data have been obtained from balloons, although the OSO-3, and more recently the OSO-7, have contributed. With the exception of CEN A, the SMC, and possibly M-87, all the sources detected at higher energies are galactic and heavily concentrated in the galactic plane. The Crab Nebula has been measured to about 500 keV in continuous emission and a component at the 33-msec pulsar period comprising about 20% of the total emission has been detected to 10 MeV. Objects such as SCO-1 and CYG-2 are characterized by an exponential spectrum, which varies over a 10-min time scale about a factor of two, and a flatter spectrum extending to above 40 keV which exhibits independent variability.

Peterson, L. E.↗
NASA NTRS1973

Galactic X-ray polarimetry and high-resolution X-ray spectroscopy.

Stellar X-ray spectroscopy and polarimetry are discussed in terms of the source parameters that can be determined through such studies and in terms of the constraints that these studies will place on theoretical models. The spectroscopic and polarimetric results that have been obtained to date are reviewed. These include the recent discovery of X-ray polarization in the Crab Nebula and the recent evidence for X-ray coronal line emission in the Cygnus Loop. Finally, the properties and predicted performance of a number of satellite-borne spectrometers and polarimeters are presented.

Novick, R.↗
NASA NTRS1973

Model studies of crosswind landing-gear configurations for STOL aircraft

A dynamic model was used to directly compare four different crosswind landing gear mechanisms. The model was landed as a free body onto a laterally sloping runway used to simulate a crosswind side force. A radio control system was used for steering to oppose the side force as the model rolled to a stop. The configuration in which the landing gears are alined by the pilot and locked in the direction of motion prior to touchdown gave the smoothest runout behavior with the vehicle maintaining its crab angle throughout the landing roll. Nose wheel steering was confirmed to be better than steering with nose and main gears differentially or together. Testing is continuing to obtain quantitative data to establish an experimental data base for validation of an analytical program that will be capable of predicting full scale results.

Stubbs, S. M.↗
NASA NTRS1973

Recent observations of cosmic gamma-rays from 10 MeV to 1 GeV

Recent observations of cosmic gamma rays made subsequent to the discovery of energetic protons from the galactic plane are discussed. The main areas covered include: (1) gamma ray emission from the plane galaxy, with emphasis on observations made in the vicinity of the galactic center, (2) gamma ray emission from the Crab nebula and its pulsar, and (3) diffuse gamma radiation.

Share, G. H.↗
NASA NTRS1973

Investigation of gamma rays from the galactic center

Data from Argentine balloon flights made to investigate gamma ray emission from the galactic center are summarized. Data are also summarized from a Palestine, Texas balloon flight to measure gamma rays from NP 0532 and Crab Nebulae.

Helmken, H. F.↗
NASA NTRS1974

Study of optical properties of X-ray sources

X-ray sources are reported for HZ Herculis, supergiant primary X-ray binary systems, and Cyg X-3. Also reported is an analysis of earlier optical and X-ray observations, along with optical coverage of the 1974 lunar occulation of the Crab Nebula.

Vandenbout, P. A.↗
NASA NTRS1973

Rotating neutron star models and pulsars

Recently developed equations of state are used to construct fully relativistic models of rotating neutron stars. All of these stable neutron star models are bound. Consideration of binding energies suggests that very-low-mass neutron stars will not be formed in supernova explosions. Some criteria for equations of state are derived from a comparison with observations. Limits for the physical parameters of the Crab pulsar are obtained. In addition, we find that cosmic-ray protons cannot be produced by pulsars.

Boerner, G.↗
NASA NTRS1973

Magnetosphere structure and radiation mechanisms of pulsars

A presentation is made of the two main models of the radiation mechanism of pulsars: the light cylinder model and the polar cap model. They have to account for gamma radiation, radio and X-ray emission, and in the case of the Crab pulsar, optical radiation. It is hypothesized that pair creation is essential for radio emission. None of the models yields a theoretical pulse-width-period distribution or braking index that correlates well with observations. A revision of the polar cap model suggests that a glitch may be present in the magnetosphere, necessitating the presence of a large centrifugal force strong enough to tear open the magnetic field lines into a Y-type configuration. This model yields a braking index in line with observations.

Roberts, D. H.↗
NASA NTRS1974

Cooling of dense stars

Some recent work on thermal properties of dense stars is described. It is now generally believed that pulsars are rotating, magnetic neutron stars (Gold, 1968). Moreover, theoretical considerations and some observational evidence (such as the speed-ups of the Crab and Vela pulsars) suggest the presence of superfluids in neutron stars. In the earlier cooling calculations the effect of magnetic fields and superfluidity was not taken into account. In the recent work, emphasis was placed on the effect of these new factors, which were expected to reduce cooling rates significantly. The new outcome may prove valuable for the understanding of pulsar and X-ray star problems.

Tsuruta, S.↗
NASA NTRS1974

Galactic X-ray sources

Data on galactic X-ray sources from rocket and balloon experiments and the UHURU satellite are reported. The outline emphasizes general discrete source models and begins with some a priori considerations about X-ray emission mechanisms and their applicability, after which contemporary data are interpreted according to these models. Topics covered include the production of X-rays by various mechanisms, source regimes, observational parameters, stellar distributions, individual stars, flare stars, supernovae and pulsars, the Crab nebula, old and young remnants, binary systems, and others.

Holt, S. S.↗