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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

A high-resolution gamma-ray and hard X-ray spectrometer for solar flare observations in Max 1991

A long duration balloon flight instrument for Max 1991 designed to study the acceleration of greater than 10 MeV ions and greater than 15 keV electrons in solar flares through high resolution spectroscopy of the gamma ray lines and hard X-ray and gamma ray continuum is described. The instrument, HIREGS, consists of an array of high-purity, n-type coaxial germanium detectors (HPGe) cooled to less than 90 K and surrounded by a bismuth germanate (BGO) anticoincidence shield. It will cover the energy range 15 keV to 20 MeV with keV spectral resolution, sufficient for accurate measurement of all parameters of the expected gamma ray lines with the exception of the neutron capture deuterium line. Electrical segmentation of the HPGe detector into a thin front segment and a thick rear segment, together with pulse-shape discrimination, provides optimal dynamic range and signal-to-background characteristics for flare measurements. Neutrons and gamma rays up to approximately 0.1 to 1 GeV can be detected and identified with the combination of the HPGe detectors and rear BGO shield. The HIREGS is planned for long duration balloon flights (LDBF) for solar flare studies during Max 1991. The two exploratory LDBFs carried out at mid-latitudes in 1987 to 1988 are described, and the LDBFs in Antarctica, which could in principle provide 24 hour/day solar coverage and very long flight durations (20 to 30 days) because of minimal ballast requirements are discussed.

Lin, R. P.↗
NASA NTRS1989

Gamma-ray lines produced by low-energy cosmic rays in SN 1987A

The Fe-56 nuclei excited by the inelastic collision of protons with the energy of around 10 MeV emit gamma rays in the same nuclear gamma-ray lines as those from the radioactive decay of Co-56. Since a very young supernova remnant like SN 1987A is most likely to accelerate cosmic rays by the shock and a possible pulsar embedded in the ejecta, this process may account for the gamma-ray lines observed from SN 1987A. The conditions required to explain the observed flux of the gamma-ray lines were investigated. It was found that this jet having a large fraction of the total kinetic energy of the supernova explosion.

Ebisuzaki, Toshikazu↗
NASA NTRS1989

Connections between X-ray and optical variability in the low mass X-ray binary 1735-444

The results of a long duration (4 day) simultaneous optical and X-ray observation of the low mass X-ray binary 1735-444 are presented. The observed X-ray and optical fluxes are correlated; the strength of this correlation is increased when allowance is made for the relatively large orbital modulation of the optical light. A simple interpretation of the optical radiation as reprocessed X-rays in a blackbody disk leads to an implausibly low disk temperature if the disk is assumed to have constant geometry. 1735-444 exhibits bimodal behavior having an X-ray spectral hardness ratio versus source intensity which is similar to that previously seen in sources such as Cyg X-2.

Corbet, R. H. D.↗
NASA NTRS1989

The solar gamma ray and neutron capabilities of COMPTEL on the Gamma Ray Observatory

The imaging Compton telescope COMPTEL on the Gamma Ray Observatory (GRO) has unusual spectroscopic capabilities for measuring solar gamma-ray and neutron emission. The launch of the GRO is scheduled for June 1990 near the peak of the sunspot cycle. With a 30 to 40 percent probability for the Sun being in the COMPTEL field-of-view during the sunlit part of an orbit, a large number of flares will be observed above the 800 keV gamma-ray threshold of the telescope. The telescope energy range extends to 30 MeV with high time resolution burst spectra available from 0.1 to 10 MeV. Strong Compton tail suppression of instrumental gamma-ray interactions will facilitate improved spectral analysis of solar flare emissions. In addition, the high signal to noise ratio for neutron detection and measurement will provide new neutron spectroscopic capabilities. Specifically, a flare similar to that of 3 June 1982 will provide spectroscopic data on greater than 1500 individual neutrons, enough to construct an unambiguous spectrum in the energy range of 20 to 200 MeV. Details of the instrument and its response to solar gamma-rays and neutrons will be presented.

Ryan, James M.↗
NASA NTRS1991

X-ray-illuminated stellar winds - Optically thick wind models for massive X-ray binaries

The work of Stevens and Kallman (1990) on the effect of accretion-powered X-rays from the neutron star on the dynamics of the line-driven stellar wind of the early-type primary is extended. Radiative force multipliers that now depend on the column of attenuating material, as well as the ionization parameter, are calculated. Optical depth effects are found to suppress the effects of X-ray ionization on the force multipliers. A number of dynamical models for the winds of massive X-ray binary systems (MXRBs) are calculated with these force multipliers. Unlike the optically thin models, self-consistent dynamical solutions are found for reasonable values of the X-ray luminosity. These solutions also reveal the presence of nonlinear mechanisms that affect wind dynamics, whereby relatively small changes in the force multipliers can lead to significant changes in the wind structure. The models find the existence of a self-consistent region of solution at an X-ray luminosity of about 10 to the 36th ergs/s and suggest the possible existence of high-luminosity states.

Stevens, Ian R.↗
NASA NTRS1990

Observing soft X-ray line emission from the interstellar medium with X-ray calorimeter on a sounding rocket

For an X-ray calorimeter working at 0.1 K, the energy resolution ideally can be as good as one eV for a practical detector. A detector with a resolution of 17 eV FWHM at 6 keV has been constructed. It is expected that this can be improved by a factor of two or more. With X-ray calorimeters flown on a sounding rocket, it should be possible to observe soft X-ray line emission from the interstellar medium over the energy range 0.07 to 1 keV. Here, a preliminary design for an X-ray calorimeter rocket experiment and the spectrum which might be observed from an equilibrium plasma are presented. For later X-ray calorimeter sounding rocket experiments, it is planned to add an aluminum foil mirror with collecting area of about 400 sq cm to observe line features from bright supernova remnants.

Zhang, J.↗
NASA NTRS1991

Can the cosmic x ray and gamma ray background be due to reflection of a steep power law spectrum and Compton scattering by relativistic electrons?

We reconsider the recent model for the origin in the cosmic X-ray and gamma-ray background by Rogers and Field. The background in the model is due to an unresolved population of AGNs. An individual AGN spectrum contains three components: a power law with the energy index of alpha = 1.1, an enhanced reflection component, and a component from Compton scattering by relativistic electrons with a low energy cutoff at some minimum Lorentz factor, gamma(sub min) much greater than 1. The MeV bump seen in the gamma-ray background is then explained by inverse Compton emission by the electrons. We show that the model does not reproduce the shape of the observed X-ray and gamma-ray background below 10 MeV and that it overproduces the background at larger energies. Furthermore, we find the assumptions made for the Compton component to be physically inconsistent. Relaxing the inconsistent assumptions leads to model spectra even more different from that of the observed cosmic background. Thus, we can reject the hypothesis that the high-energy cosmic background is due to the described model.

Zycki, Piotr T.↗
NASA NTRS1992

Search for periodic gamma-ray emission from Cygnus X-3 by the EGRET telescope on the Compton Gamma-Ray Observatory

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory observed the Cygnus region of the Galaxy during the periods 1991 May 30-June 8 and 1991 August 8-15. We report on a periodicity analysis of the gamma rays originating from the direction of Cygnus X-3. This analysis showed no evidence of periodic modulation during these observations of the gamma-ray emission at the approximately 4.8 hr period observed at X-ray wavelengths.

Michelson, P. F.↗
NASA NTRS1991

The UCSD high energy X-ray timing experiment cosmic ray particle anticoincidence detector

The HEXTE, part of the X-Ray Timing Explorer (XTE), is designed to make high sensitivity temporal and spectral measurements of X-rays with energies between 15 and 250 keV using NaI/CsI phoswich scintillation counters. To achieve the required sensitivity it is necessary to provide anticoincidence of charged cosmic ray particles incident upon the instrument, some of which interact to produce background X-rays. The proposed cosmic ray particle anticoincidence shield detector for HEXTE uses a novel design based on plastic scintillators and wavelength-shifter bars. It consists of five segments, each with a 7 mm thick plastic scintillator, roughly 50 cm x 50 cm in size, coupled to two wavelength-shifter bars viewed by 1/2 inch photomultiplier tubes. These segments are configured into a five-sided, box-like structure around the main detector system. Results of laboratory testing of a model segment, and calculations of the expected performance of the flight segments and particle anticoincidence detector system are presented to demonstrate that the above anticoincidence detector system satisfies its scientific requirements.

Hink, P. L.↗
NASA NTRS1993

Optical and X-ray observations of the low-mass X-ray binary EXO 0748-676

Optical and X-ray observations of EXO-676 in late March 1989 are presented. Our optical observations provide some support for the previously observed correlation between the mean optical brightness and light curve morphology. Unexpectedly, the mean X-ray and optical flux levels during this period do not reflect similar system states. The optical counterpart is found to be in an intermediate to low state, while X-ray data imply a bright (high) state. The changed relationship between optical and X-ray fluxes is evidence showing that EXO 0748-676 has possibly evolved. We fail to find correlated variability in simultaneous X-ray and optical observations. The lack of covariability is attributed to the limited simultaneous coverage of the source and/or significant geometric modulation in the optical light curve.

Thomas, Brian↗
NASA NTRS1992

Low-mass X-ray binaries and gamma-ray bursts

More than twenty years after their discovery, the nature of gamma-ray burst sources (GRBs) remains mysterious. The results from BATSE experiment aboard the Compton Observatory show however that most of the sources of gamma-ray bursts cannot be distributed in the galactic disc. The possibility that a small fraction of sites of gamma-ray bursts is of galactic disc origin cannot however be excluded. We point out that large numbers of neutron-star binaries with orbital periods of 10 hr and M dwarf companions of mass 0.2-0.3 solar mass are a natural result of the evolution of low-mass X-ray binaries (LMXBs). The numbers and physical properties of these systems suggest that some gamma-ray burst sources may be identified with this endpoint of LMXB evolution. We suggest an observational test of this hypothesis.

Lasota, J. P.↗
NASA NTRS1994

Large area soft x-ray collimator to facilitate x-ray optics testing

The first objective of this program is to design a nested conical foil x-ray optic which will collimate x-rays diverging from a point source. The collimator could then be employed in a small, inexpensive x-ray test stand which would be used to test various x-ray optics and detector systems. The second objective is to demonstrate the fabrication of the x-ray reflectors for this optic using lacquer-smoothing and zero-stress electroforming techniques.

Espy, Samuel L.↗
NASA NTRS1994

The optical and X-ray content of the 1992 May 1 gamma-ray burst error box

A gamma-ray burst which occurred on 1992 May 1 was observed by three spacecraft in the third interplanetary network, and rapidly localized to a small error box. The coordinates were promptly circulated to a wide astronomical community, and radio, optical, and X-ray counterpart searches were carried out. A weak X-ray source was found in the error box, and two radio sources are discovered outside the error box, but in alignment with the X-ray source. The X-ray source position contains approximately 25 optical objects down to 23d magnitude. We discuss the prospects for identifying the burster counterpart.

Hurley, K.↗
NASA NTRS1994

The isotopic composition of cosmic-ray beryllium and its implication for the cosmic ray's age

We report a new measurement of the cosmic-ray isotopic composition of beryllium in the low-energy range from 35 to 113 MeV per nucleon. This measurement was made using the High Energy Telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1991. In this overall time period of 14 years the average solar modulation level was about 500 MV. The cosmic-ray beryllium isotopes were completely separated with an average mass resolution sigma of 0.185 amu. The isotope fractions of Be-7, Be-9, and Be-10 obtained are 52.4 +/- 2.9%, 43.3 +/- 3.7%, and 4.3 +/- 1.5%, respectively. The measured cosmic-ray abundances of Be-7 and Be-9 are found to be in agreement with calculations based on standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the recent cross sections of the New Mexico-Saclay collaboration. From our observed ratio Be-10/Be = 4.3 +/- 1.5% we deduce an average interstellar density of about 0.28 (+0.14, -0.11) atoms/cu cm, and acosmic-ray lifetime for escape of 27 (+19, -9) x 10(exp 6) years. The surviving fraction of Be-10 is found to be 0.19 +/- 0.07. Modifications to the conclusions of the Leaky-Box model when a diffusion + convection halo model for propagation is used are also considered.

Lukasiak, A.↗
NASA NTRS1994

Constraints on hot star X-ray source characteristics from combinded analysis of X-ray and UV observations

Results from wind ionization calculations are presented which show how the P-Cygni profiles of 'superionized' species such as O VI can provide information about the X-ray source characteristics of early-type stars. Using detailed radiative and atomic physics models, we find that a significant source of X-ray emission from zeta Pup comes from a region in the wind located within rougly 1 to 2 stellar radii of the photosphere. Our results suggest that X-rays sources in which emission occurs exclusively at large radii (r greater than or approximately equal to a few R(sub *)) are inconsistent with UV P-Cygni profiles for O VI. Instead, we find that X-ray emission from shocks distributed throughout the lower regions of the wind (r approximately equal to 1-2 R(sub *)) is consistent with both X-ray and UV data, as well as mass loss rates deduced from radio and H-alpha observations.

Macfarlane, J. J.↗
NASA NTRS1996

The Integrated X-Ray Spectrum of Galactic Populations of Luminous Supersoft X-Ray Sources

We compute the composite X-ray spectrum of a population of unresolved SSS's in a spiral galaxy such as our own or M31. The sources are meant to represent the total underlying population corresponding to all sources which have bolometric luminosities in the range of 10(exp 37) - 10(exp 38) ergs/s and kT on the order of tens of eV. These include close-binary supersoft sources, symbiotic novae, and planetary nebulae, for example. In order to determine whether the associated X-ray signal would be detectable, we also 'seed' the galaxy with other types of X-ray sources, specifically low-mass X-ray binaries (LMXB's) and high-mass X-ray binaries (HMXB's). We find that the total spectrum due to SSS's, LMXB's, and HMXB's exhibits a soft peak which owes its presence to the SSS population. Preliminary indications are that this soft peak may be observable.

DiStefano, R.↗
NASA NTRS1997

Low-state gamma-ray emission from blazars and the gamma-ray background

The contribution of flat spectrum radio sources (FSRS) or blazars to the diffuse gamma ray background is examined. The basic assumptions of the investigation are: the existence of steady state gamma ray emission at the energetic gamma ray experiment telescope (EGRET) instrument energy band from the entire population of the FSRS; a proportionality between the FSRS' gamma ray luminosities and radio luminosities; and the production of the diffuse gamma ray background by the ensemble of blazars. Under these assumptions, the estimated average value of the proportionality constant in the luminosity relationship (vF(sub v))(sub 100 MeV) = f(vF(sub v))(sub 5 GHz) is approximately 70, compared to a mean observed value of 750. The implications of this result for the active galactic nuclei models are considered.

Kazanas, Demosthenes↗
NASA NTRS1997

Cosmic Ray Induced Degradation in X-Ray Detectors On Board the Near Earth Asteroid Rendezvous Spacecraft

The Near-Earth Asteroid Rendezvous (NEAR) mission is the first in NASA's new Discovery Program to explore the solar system. Launched in February 1996, the NEAR spacecraft will take a long cruise flight arriving at the asteroid 433 Eros in January 1999 for a one year orbiting survey operation. This long exposure to the space environment has already proven to be an additional complication for the x-ray spectrometer. The asteroid pointing detectors for the x-ray spectrometer are three gas-filled proportional counters with resolving power in the range of 1 keV. Therefore, to resolve the important but closely spaced magnesium, aluminum and silicon k alpha lines( 1.255, 1.487, 1.739 keV respectively), magnesium and aluminum balanced filters are used on two of the detectors. The x-ray florescence from the surface of Eros is stimulated by solar x-rays. A proportional counter and a silicon PIN detector are used to monitor the solar incident x-ray flux. The proportional counters are single wire gas filled beryllium lined steel tubes operating at about 1100 volt. The 25 cm(exp 2) optical window is one mil. thick beryllium. To define the detector's active region, two boron nitride disks were incorporated in the tube just outside window area. It appears from the space flight data that the space environment is creating a charge on these boron nitride disks which ultimately distorts the tube gain and resolution. This broadening of the photo peak makes it more difficult to identify weak peaks and so degrades the statistical accuracy for some very important elements such as sulfur, calcium and iron (2.307, 3.690, 6.403 keV respectively). If the broadening is severe enough in the low energy region, counts will be lost as the photo peak spreads below the lower level discriminator (0.7 keV).

Floyd, S. R.↗