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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 181 records · Page 10
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NASA NTRS1977

SAS-2 observations of high energy gamma rays from discrete sources

The SAS-2 identified six localized high energy (greater than 35 MeV) gamma ray sources. Four of these are the radio pulsars, PSR 0531+21, PSR 0833-45, PSR 1818-04, and PSR 1717-46 discovered in a search of 75 radio pulsars. The fact that only one of these is observed in X-rays, and the significant differences in pulse profiles in the gamma ray and radio observations, leads to the speculation that different mechanisms are involved.

Kniffen, D. A.↗
NASA NTRS1973

Prospects for nuclear-gamma-ray astronomy

Two sources of gamma rays from outside the solar system are considered. In particular, nucleosynthesis-supernova explosion and inelastic collisions are discussed.

Clayton, D. D.↗
NASA NTRS1992

Gamma ray bursts from extragalactic sources

The properties of gamma ray bursts of classical type are found to be explicable in terms of high speed collisions between stars. A model is proposed in which the frequency of such collisions can be calculated. The model is then applied to the nuclei of galaxies in general on the basis that galaxies, or at least some fraction of them, originate in the expulsion of stars from creation centers. Evidence that low level activity of this kind is also taking place at the center of our own Galaxy is discussed. The implications for galactic evolution are discussed and a negative view of black holes is taken.

Hoyle, Fred↗
NASA NTRS1978

Distance limit for a class of model gamma-ray burst sources

It is pointed out that MeV photons have actually been observed in bursts. These observations imply that the nonrelativistic sources cannot be further away than a few kpc from the sun and, therefore, must be galactic. The 27 April 1972 event observed by Apollo 16 shows at higher energies a power law spectrum with a possible line feature around 4 MeV. The optical depth of a homogeneous, isotropic radiation field is estimated with the aid of formulae used by Nikishov (1962) and Jauch and Rohrlich (1955). On the basis of an investigation of the various factors involved, it is tentatively suggested that the gamma-ray bursts which have been detected are galactic, but are in the majority of the cases not connected with unique irreversible star transformation. It appears also unlikely that the gamma-ray bursts are connected with galactic novae.

Schmidt, W. K. H.↗
NASA NTRS1993

Gasdynamics of relativistically expanding gamma-ray burst sources - Kinematics, energetics, magnetic fields, and efficiency

We calculate both analytically and numerically the evolution of highly relativistic fireballs through the stages of free expansion and coasting, and determine the dependence of the thermodynamic and radiation variables in the comoving and laboratory flames. The dynamics and the comoving geometry change at the (lab) expansion factors r/r(0) greater than eta and r/r(0) greater than eta-squared, respectively, where eta = E(0)/M(0)c-squared is the initial Lorentz factor. In the lab, the gas appears concentrated in a thin shell of width r(0) until r/r(0) of less than about eta-squared, and increases linearly after that. Magnetic fields may have been important in the original impulsive event. We discuss their effect on the fireball dynamics and also consider their effects on the radiation emitted when the fireball runs into an external medium and is decelerated. The inverse synchro-Compton mechanism can then yield high radiative efficiency in the reverse shock (and through turbulent instabilities and mixing also in the forward blast wave), producing a burst of nonthermal radiation mainly in the MeV to GeV range. The energy and duration depend on eta, the magnetic field strength, and the external density, and can match the range of properties observed in cosmic gamma-ray bursts.

Meszaros, P.↗
NASA NTRS1976

COS-B observations of localised sources of gamma-ray emission

In October 1975 the high energy gamma ray flux from the Vela pulsar was measured by COS-B to be 1.6 to 2.1 times higher than the flux measured by SAS-2 in 1973. The existence is confirmed of a second region of enhanced radiation in the galactic anticenter in addition to that from the Crab pulsar.

Mayer-Hasselwander, H.↗
NASA NTRS1977

COS-B observations of localized sources of gamma-ray emission

In October 1975, the high-energy gamma-ray flux from the Vela pulsar measured by COS-B was found to be 1.6 to 2.1 times higher than the flux measured by SAS-2 in 1973. This factor is too large to be accounted for by error in the COS-B calibration or analysis. This is supported by a comparison of the COS-B measurement of the narrow-line component from the galactic center region with the flux derived from the measurements of SAS-2; the COS-B flux comes out about 15 percent lower than the SAS-2 figure. It is interesting to note that a glitch in the pulsar period took place about 1 month prior to the COS-B observation; the previous glitch occurred about 1.5 years before the SAS-2 observation. The increased rotational energy loss after the glitch cannot simply explain the increased gamma-ray luminosity. If the two phenomena are related, the gamma-ray emission, absorption, or beaming process must be extremely sensitive to changes in rotational parameters. The existence is confirmed of a second region of enhanced radiation in the galactic anticenter in addition to that from the Crab pulsar.

Source record↗
NASA NTRS1977

Al-26 - A galactic source of gamma-ray line emission

A detectable gamma-ray line at 1.809 MeV results from the decay of Al-26 in the interstellar medium if this isotope is synthesized in supernovae with abundance of about 0.001 relative to Mg-26. The expected intensity from the direction of the galactic center is approximately 0.0001 photon/sq cm/sec per sr, and the line width is less than 3 keV. This intensity is comparable to the intensities of the other strongest gamma-ray lines resulting from processes of nucleosynthesis at 0.847 MeV from Fe-56, 1.156 MeV from Ca-44, and 1.173 and 1.332 MeV from Ni-60. But the width of the line from Al-26 decay is an order of magnitude smaller than that of either the 0.847- or the 1.156-MeV lines, and hence this line should be much more easily observable with high-resolution detectors.

Ramaty, R.↗
NASA NTRS1990

Cyclotron lines - The next 100 years

The relationship between cyclotron lines and other spectral features of stars requires a numerical construction of theoretical spectra and numerical comparison of simulated and actual data. These techniques - combined with supercomputer technology - can enhance the study of X-ray and gamma-ray sources. The present understanding of the behavior of the rays is set forth, and the application of data from cyclotron line formation is suggested to examine accreting X-ray sources and gamma-ray bursts in neutron stars.

Wasserman, Ira↗
NASA NTRS1994

The Compton Gamma Ray Observatory

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.↗
NASA NTRS2007

Monitoring the Low-Energy Gamma-Ray Sky Using Earth Occultation with GLAST GBM

Long term all-sky monitoring of the 20 keV - 2 MeV gamma-ray sky using the Earth occultation technique was demonstrated by the BATSE instrument on the Compton Gamma Ray Observatory. The principles and techniques used for the development of an end-to-end earth occultation data analysis system for BATSE can be extended to the GLAST Gamma-ray Burst Monitor (GBM), resulting in multiband light curves and time-resolved spectra in the energy range 8 keV to above 1 MeV for known gamma-ray sources and transient outbursts, as well as the discovery of new sources of gamma-ray emission. In this paper we describe the application of the technique to the GBM. We also present the expected sensitivity for the GBM.

Case, G.↗
NASA NTRS2010

A Unique Outside Neutron and Gamma Ray Instrumentation Development Test Facility at NASA's Goddard Space Flight Center

An outside neutron and gamma ray instrumentation test facility has been constructed at NASA's Goddard Space Flight Center (GSFC) to evaluate conceptual designs of gamma ray and neutron systems that we intend to propose for future planetary lander and rover missions. We will describe this test facility and its current capabilities for operation of planetary in situ instrumentation, utilizing a l4 MeV pulsed neutron generator as the gamma ray excitation source with gamma ray and neutron detectors, in an open field with the ability to remotely monitor and operate experiments from a safe distance at an on-site building. The advantage of a permanent test facility with the ability to operate a neutron generator outside and the flexibility to modify testing configurations is essential for efficient testing of this type of technology. Until now, there have been no outdoor test facilities for realistically testing neutron and gamma ray instruments planned for solar system exploration

Bodnarik, J.↗
NASA NTRS1994

The first energetic gamma-ray experiment telescope (EGRET) source catalog

In this catalog the results related to high-energy gamma-ray sources obtained from the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory are summarized for the period from 1991 April 22 to 1992 November 17, called phase 1. This phase of the Compton Observatory mission was devoted to an all-sky survey. Tables are included for the following EGRET results: solar flares with detected gamma radiation; pulsars; sources with absolute value of b is less than 10 deg, gamma-ray bursts; normal galaxies; clusters of galaxies; positive detections of radio-loud quasars and BL Lac objects; marginal detections of radio-loud quasars and BL Lac objects; upper limits for radio-loud quasars and BL Lac objects; upper limits for Seyfert galaxies and selected radio-quiet quasars, and other sources with absolute value of b is greater than or equal to 10 deg the Galactic plane. There is also a table relating the dates of the observations to the Compton Observatory viewing period numbers to assist in referencing the observations.

Fichtel, C. E.↗
NASA NTRS1987

On the possibility of observing cosmic ray sources in high energy gamma rays

If cosmic rays are accelerated by strong shocks, then cosmic ray sources should be characterized by spectra, dN/dE alpha E exp -(2.0-2.2), reflecting the strength of those shocks. This is expected from the 'standard leaky box' model of cosmic ray propagation in which the source spectra are harder than the observed spectra because higher energy particles have shorter residence times in the galactic magnetic fields. Furthermore, data on cosmic ray nucleons suggest that these sources might be surrounded by material. If the latter is true, such sources should be observable in gamma rays at energies beyond 1 GeV where the angular resolution of gamma-ray telescopes is optimized and the background is significantly reduced. For identified sources, the source location accuracy can be shown to improve with increasing energy in spite of the decreasing statistics, as long as the gamma-ray spectrum is harder than dN/dE alpha E exp -gamma. A Monte Carlo model is used to predict the photon spectra which would be expected from cosmic ray sources under varying assumptions about the strength of the shocks in the acceleration region.

Ormes, J. F.↗
NASA NTRS1985

Search for TeV gamma rays from extragalactic sources and the Galactic Center

The Ooty atmospheric Cerenkov array was used in 1982-83 to see if the galactic center and the extra-galactic sources 3C 273, Centaurus A emit gamma rays at TeV energies. The ON/OFF method was used wherein the source was tracked for 16 minutes and immediately afterwards, a background region in the same zenith angle range was tracked for the next 16 minutes. Data were taken for approx 15 hours (55 scans) on 3C273, approx 7 hours (26 scans) on Cen A and 5 hours (19 scans) on galactic center. A preliminary analysis involving direct comparison of total rates on and off the source shows no significant excess from any of these orbits. Results of detailed analysis using different energy thresholds are presented.

Bhat, P. N.↗