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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 NTRS1975

Observations of the Circinus X-1 region

The X-ray telescope on board the OSO-7 satellite has provided observations of the Cir X-1 region for over 110 days between December 1971 and March 1973. Although statistically significant fluctuations in the 7- to 11-keV flux were measured, no periodicities in the range between 5 hours and 100 days were found to an upper limit of about 40 percent amplitude. Intensities in the 7- to 57-keV range show variability by a factor of approximately 25 and changes in the spectral shape reflected by a number spectral index varying from about 1.1 to about 3.0. There is a positive correlation between intensity and spectral shape, with a steeper spectrum at times of peak intensity. Although power-law, exponential, and blackbody spectral shapes are equally good fits to these data alone, examination of all the available data appears to rule out a simple blackbody spectrum, at least at times of maximum intensity.

Baity, W. A.↗
NASA NTRS1975

Mineralogy, petrology, and geochemistry of the lunar samples

The geochemistry of the bulk moon is considered, taking into account the large-scale chemical view of the lunar surface which has been obtained with the aid of three remote sensing experiments utilizing X-ray fluorescence, a gamma-ray spectrometer, and visible and near infrared reflectance measurements. Attention is also given to the regolith, the mare basins, and the lunar highlands and crust.

Warner, J.↗
NASA NTRS1975

Molecular hydrogen in the Galaxy and galactic gamma rays

Recent surveys of 2.6-cm CO emission and 100-MeV gamma-radiation in the galactic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H2 in the inner Galaxy. Both the gamma-ray and CO data suggest a prominent ring or arm consisting of cool clouds of H2 at a galactocentric distance of about 5 kpc with a mean total hydrogen density equivalent to approximately 5 atoms per cu cm. Estimates are made of column densities of H2 at 0 deg galactic longitude and are compared with estimates from infrared and X-ray absorption measurements. These estimates are all consistent, indicating that H2 is far more abundant than H I in the inner Galaxy and is the key to a more satisfactory explanation of the gamma-ray observations than previous suggestions. The importance of H2 in understanding galactic gamma-ray observations is also reflected in the correlation of galactic-latitude distribution of gamma-rays and dense dust clouds. The deduced cosmic-ray distribution inferred from the calculations is similar to that of galactic supernova remnants, suggesting a galactic origin for most cosmic rays.

Stecker, F. W.↗
NASA NTRS1976

Vignetting characteristics of the S-056 X-ray telescope

A ray trace analysis of the vignetting characteristics of the S-056 X ray telescope is presented. The relative energy is calculated in the spot formed in the focal plane of the S-056 X ray telescope by an off axis point source at infinity for off axis angles of 0, 1, 2, ..., 35 arc minutes. At each off axis angle, the relative energies are evaluated using theoretical X ray reflectivity curves for wavelengths of 8.34 A, 17.57 A, and 27.39 A, and also using an experimental X ray reflectivity curve for 8.34 A. The effects of vignetting due purely to the geometry of the S-056 optical system are evaluated separately, as well as jointly with the effects of mirror reflectivity.

Foreman, J. W., Jr.↗
NASA NTRS1977

Backscatter of hard X-rays in the solar atmosphere

The solar photosphere backscatters a substantial fraction of the hard X rays from solar flares incident upon it. This reflection was studied using a Monte Carlo simulation which takes into account Compton scattering and photo-electric absorption. Both isotropic and anisotropic X ray sources are considered. The bremsstrahlung from an anisotropic distribution of electrons are evaluated. By taking the reflection into account, the inconsistency is removed between recent observational data regarding the center-to-limb variation of solar X ray emission and the predictions of models in which accelerated electrons are moving down toward the photosphere.

Bai, T.↗
NASA NTRS1977

Design, fabrication and expected performance of the HEAO-B X ray telescope

The X-ray telescope of the second High Energy Astronomy Observatory (HEAO-B) is described. The design consists of four concentric paraboloid/hyperboloid pairs. Focal length is 3.44 meters, paraboloid diameters vary from 580-336 mm, grazing angles vary from 70 to 40 arcmin for paraxial rays, segment lengths are 511 mm. The reflecting surfaces are nickel-coated fused quartz and the resolution is limited by assembly errors (for small field angles) and design aberrations (for large field angles). The local slope, roundness, and surface roughness are identified as the primary optical tolerances connected with the individual elements.

Van Speybroeck, L. P.↗
NASA NTRS1979

Observations of pulsating X-ray binaries 4U0900-40 and 4U1223-62

A sounding-rocket observation of the pulsating X-ray binaries 4U 0900-40 (Vela X-1) and 4U 1223-62 (GX301-2, Wray 977) over the energy range from 0.5 to 27 keV is reported. No short-time-scale periodicities in the range from 2 msec to 20 sec are found for either source, although both exhibit some minor flaring activity on time scales of a few seconds. The data for Vela X-1 suggest that the time-averaged spectra are complex and that the pulse-resolved spectra are also complex and variable, with significant fluctuations above 10 keV. When compared with other observations at different epochs, the spectral data for 4U 1223-62 confirm large variability in both intensity and spectral characteristics. It is concluded that the intrapulse changes observed in the spectral behavior of Vela X-1 must reflect changes in the surface magnetic fields and the plasma flows near the neutron star.

Ku, W. H.-M.↗
NASA NTRS1983

Associations between coronal mass ejections and soft X-ray events

The association between white light coronal mass ejections (CMEs) and full-disk X ray events have been examined as a function of X ray duration during the recent years of high sunspot activity (1979-1981). On a time scale of hours, no duration interval has been found that separates X ray events into two distinct classes depending on whether or not they have associated CMEs. Rather, the tendency for long-duration X ray events to have associated CMEs reflects the fact that, as X ray duration increases, the differential distribution of events without CMEs falls off faster than the distriution of X ray events with CMEs.

Sheeley, N. R., Jr.↗
NASA NTRS1991

Telescope Would Image X And Gamma Rays

Proposed telescope forms images of sources of gamma rays, hard x rays, and soft x rays. Contains reflecting, grazing-incidence reflectors. Multiple coaxial nested pairs used to form images simultaneously at multiple gamma-ray or hard x-ray energies or enhance collection area at single photon energy. Conceived for use in astrophysical studies in outer space. With modifications, used in terrestrial laboratory vaccum systems to image x or gamma rays from pulsed plasmas.

Hoover, Richard B.↗
NASA NTRS1989

Solar flare hard and soft x ray relationship determined from SMM HXRBS and BCS data

The exact nature of the solar flare process is still somewhat a mystery. A key element to understanding flares if the relationship between the hard x rays emitted by the most energetic portions of the flare and the soft x rays from other areas and times. This relationship was studied by comparing hard x ray light curved from the Hard X-Ray Burst Spectrometer (HXRBS) with the soft x ray light curve and its derivation from the Bent Crystal Spectrometer (BCS) which is part of the X-Ray Polychrometer (XRP), these instruments being on the Solar Maximum Mission spacecraft (SMM). Data sample was taken from flares observed with the above instruments during 1980, the peak of the previous maximum of solar activity. Flares were chosen based on complete coverage of the event by several instruments. The HXRBS data covers the x ray spectrum from about 25 keV to about 440 keV in 15 spectral channels, while the BCS data used covers a region of the Spectrum around 3 angstroms including emission from the Ca XIX ion. Both sets of data were summed over their spectral ranges and plotted against time at a maximum time resolution of around 3 seconds. The most popular theory of flares holds that a beam of electrons produces the hard x rays by bremsstrahlung while the soft x rays are the thermal response to this energy deposition. The question is whether the rate of change of soft x ray emission might reflect the variability of the electron beam and hence the variability of the hard x rays. To address this, we took the time derivative of the soft x ray light curve and compared it to the hard flares, 12 of them showed very closed agreement between the soft x ray derivative and the hard x ray light curve. The other five did not show this behavior but were similar to each other in general soft x ray behavior. Efforts to determine basic differences between the two kinds of flares continue. In addition the behavior of soft x ray temperature of flares was examined.

Toot, G. David↗
NASA NTRS1991

X-ray echoes from gamma-ray bursts

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed.

Dermer, Charles D.↗
NASA NTRS1992

An ionized accretion disk in Cygnus X-1

Results of an analysis of archival Exosat and HEAO 1-A2 observations of Cyg X-1 are presented. It is found, in agreement with Ebisawa (1991), that the X-ray spectrum of Cyg X-1 exhibits a 'high-energy excess' above 8 keV, similar to that seen in Ginga spectra of AGN. It is shown, on the basis of a likelihood ratio test, that the data are significantly better fit by a Compton reflection model than by a partial covering model. Even with the energy resolution of the Exosat GSPC, it is found that the derived iron line energy and shape are very dependent on the continuum model used. The best-fit temperature for a Suniaev-Titarchuk Comptonization model is found to be significantly larger than that found in previous analyses based primarily on data in the 30-140 keV band. This suggests that the 5-50 keV continuum is not well fit by the same spectrum form applicable at high energies and that a multiple temperature thermal Compton model is necessary to fit the broadband data.

Done, C.↗
NASA NTRS1993

Radiation from magnetized accretion disks in active galactic nuclei

We present a model of AGN based on accretion disks around 10 exp 8 solar mass black holes, which incorporates a strong magnetic field in the disk, with loops above the disk in which B is about 100 G. The magnetic energy in the loops dissipates, accelerating electrons to relativistic energies. The electrons emit synchrotron and inverse-Compton radiation, much of which is reflected or scattered by gas in the disk. We calculate the emitted spectrum from infrared to gamma rays. Of the total emission, 23 percent goes into a nu exp -1 power law and 77 percent into thermal radiation at 24,000 K (due to the disk, which is heated by nonthermal radiation and energetic ions). The model accounts quantitatively for the X-ray and gamma-ray backgrounds, and it accounts qualitatively for certain features observed in individual AGNs: a far-infrared cutoff, a minimum at a few microns, the ultraviolet bump, the Compton reflection bump at about 30 keV, and a gamma-ray tail.

Field, G. B.↗
NASA NTRS1993

Resolving the iron K line in Cygnus X-2 - An observation with BBXRT

The Astro-1 Space Shuttle payload's Broad Band X-ray telescope has been used to obtain high-quality, moderate-resolution spectroscopy of Cygnus X-2 which allow the resolving of the physical width of the 6.7 keV Fe K-alpha feature with a factor-of-4 energy resolution improvement over past experiments. Three possible sites are noted for the Fe K-alpha emission: the accretion disk, its corona, and the source itself. It is judged that reflection from the accretion disk can generate a line of the observed energy, width, and equivalent width, provided that the disk surface is highly ionized.

Smale, A. P.↗
NASA NTRS1991

Organometallic chemical vapor deposition and characterization of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates

In this paper, we report the epitaxial growth of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates by open tube OMCVD. The chemical composition of the alloys characterized by energy dispersive X-ray spectroscopy shows that alloys with x up to 0.13 can be deposited on (001) GaP. Epitaxial growth with mirror smooth surface morphology has been achieved for x less than or equals to 0.05. Selected area electron diffraction pattern of the alloy shows that the epitaxial layer crystallizes in the chalcopyrite structure with relatively weak superlattice reflections indicating certain degree of randomness in the cation sublattice. Hall measurements show that the alloys are p-type, like the unalloyed films; the carrier concentration, however, dropped about 10 times from 2 x 10 exp 18 to 2 x 10 exp 17/cu cm. Absorption measurements indicate that the band tailing in the absorption spectra of the alloy has been shifted about 0.04 eV towards shorter wavelength as compared to the unalloyed material.

Xing, G. C.↗
NASA NTRS1993

Organometallic chemical vapor deposition and characterization of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates

The epitaxial growth of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates by open tube organometallic chemical vapor deposition (OMCVD) is reported. The chemical composition of the alloys characterized by energy dispersive X-ray spectroscopy shows that alloys with x up to 0.13 can be deposited on (001) GaP. Epitaxial growth with mirror smooth surface morphology was achieved for x less than or equal to 0.05. Transmission electron microscopy (TEM) micrographs of these alloys show specular epitaxy and the absence of microstructural defects indicating a defect density of less than 10(exp 7) cm(sup -2). Selected area electron diffraction pattern of the alloy shows that the epitaxial layer crystallizes in the chalcopyrite structure with relatively weak superlattice reflections indicating certain degree of randomness in the cation sublattice. Hall measurements show that the alloys are p-type, like the unalloyed films; the carrier concentration, however, dropped about 10 times from 2 x 10(exp 18) to 2 x 10(exp 17) cm(sup -3). Absorption measurements indicate that the band tailing in the absorption spectra of the alloy was shifted about 0.04 eV towards shorter wavelength as compared to the unalloyed material. Diodes fabricated from the n(+)-GaP/p-ZnSiP2-ZnGeP2-Ge heterostructure at x = 0.05 have a reverse break-down voltage of -10.8 V and a reverse saturation current density of approximately 6 x 10(exp -8) A/sq cm.

Xing, G. C.↗
NASA NTRS1993

AXAF-I ghost ray study: On orbit case

The problem of baffles for control of singly reflected (and nonreflected) ghost rays is considered. The theory of baffle design for Wolter Type I grazing incidence optics is reviewed, and a set of sample baffle parameters is obtained subject to the assumptions of nominal mirror figures and perfect manufacture and alignment of baffles. It is found that baffles forward of the optics (in the thermal precollimator) and between the mirror elements (at the CAP) are sufficient to allow the simultaneous ghost image and vignetting requirements to be satisfied for HRMA shells P1H1, P3H3, and P4H4. However, these baffles are not sufficient for the innermost shell P6H6; at best the requirements are slightly violated and there is no margin for tolerances. The addition of a baffle interior to the P6 space at an axial station about one third of the way forward from the aft end of the paraboloid will allow the ghost ray and vignetting requirements to be met. The minimum ghost ray angles and the vignetting angles are sensitive functions of the baffle positions and radii; tolerances of considerably better than 1 mm will be required. The sensitivities are coupled and correlated; further investigations should be undertaken in order to obtain baffle parameters which, combined with likely achievable tolerances, will minimize the risk of the vignetting/ghost ray requirements not being met. The lightweight carbon-epoxy composite used for thermal baffles has insufficient X-ray opacity to be a suitable material for construction of the controlling X-ray baffles; further study is needed to determine an appropriate material and to investigate its thermal and mechanical implications.

Gaetz, T. J.↗
NASA NTRS1995

Far-ultravoilet and optical spectrscopy of the detached white dwarf-M binary RE J1629+780

We present optical and far-ultraviolet observations, including IUE high- and low-dispersion spectroscopy, of the (DA2+dM4-5) close binary, RE J1629+780, a very bright ROSAT EUV source. The optical data reveal emission reversals in the cores of the Balmer lines, which vary in strength but reveal no evidence of wavelength shifts reflecting orbital motion, suggesting that the red dwarf and the white dwarf are widely separated. Thus it is unlikely that irradiation plays a dominant role in the activity of the red dwarf. One dramatic increase in the intensity of the H-beta emission strength in the course of one hour indicates that the observed intensity variations are most likely related to flare activity on the red dwarf. Our analysis of Balmer and Lyman alpha features yield T(sub eff) = 42,500 +/- 1300 K and log g = 7.6 +/- 0.3 for the DA2 white dwarf, which is consistent with the overall 900 to 3200 A energy distribution derived from Voyager and IUE low-dispersion spectra. Our analysis of three IUE echelle spectra reveal numerous lines of interstellar origin. Using a total of 13 interstellar matter (ISM) features we find a mean radial velocity of -13.57 +/- 1.66 km/s for the interstellar features. However, we found no evidence of trace metal absorbers levitated or accreted in the white-dwarf photosphere nor any evidence of circumstellar or wind features. We estimate a lower limit hydrogen layer mass of 2.1 x 10(exp -15) solar mass for a stratified atmosphere based upon the nondetection of He II (1640). Tighter constraints on the helium abundance and the hydrogen layer mass, from EUV and X-ray data, are presented for both homogeneous and stratified atmospheric configurations.

Sion, Edward M.↗