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NASA NTRS1979

Positron production by pulsars

Analytical calculations based on the 'polar-cap light-cylinder' (PCLC) (Sturrock, 1971a) and 'polar-cap force-balance' (PCFB) (Roberts and Sturrock, 1972,3) pulsar models show that in either case the intensity of the 511 keV gamma-ray line from the galactic center can be explained as the result of the annihilation of positrons produced by pulsars. The Crab pulsar (braking index approximately 2.5) is estimated to have a power budget of 10 to the 38th ergs/s, and to produce a total number of 10 to the 51.7th positrons. It is suggested that positron annihilation can be supplied by pulsars if the birthrate of pulsars in the galactic center is 10 to the -8.2nd/s.

Sturrock, P. A.↗
NASA NTRS1980

Gamma rays from Penrose powered black holes in Centaurus A, 3C 273, and NGC 4151

Gamma-ray observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC spectrum is attributed to Penrose Compton scattering, and the absence of an MeV break in the spectra of Cen A and 3C 273 implies Penrose pair production. Central black hole masses of tens of millions of solar masses for NGC 4151 and Cen A, and tens of billions of solar masses for 3C 273, are obtained. Attention is also given to accretion rate, the efficiency of accretion, QSOs and Seyferts.

Kafatos, M.↗
NASA NTRS1980

Energetic particles in solar flares

The various manifestations of energetic particles in solar flares are examined, and possible mechanisms for the acceleration of these particles are considered. Hard X-ray observations and possible mechanisms for the production of the dominant form of solar energetic particles, electrons with energies between 10 and 100 keV, are discussed, with consideration of thin-target models, thick-target models and thick-target models with reverse currents, and first-phase acceleration mechanisms for energetic electrons emitting impulsive microwave and fast-drift Type III radio bursts as well as impulsive hard X rays, which are detected themselves 20 min after the flare at 1 AU are considered. Radio evidence on the number, energy and pitch-angle distributions of energetic particles produced during solar flares is summarized, and observations at 1 AU of proton and electron energy spectra, the proton/electron ratio and energetic particle events rich in He-3 from solar flares are discussed. Finally, consideration is given to gamma-ray evidence of nuclear reactions in flares and white-light flares

Ramaty, R.↗
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

Discovery of a compact X-ray source at the center of the supernova remnant RCW 103

A point source of X-ray emission has been detected at the center of the supernova remnant RCW 103 using the Einstein Observatory. The 10 arcsec radius error circle is centered at alpha 16h13m47.8s, delta = -50 deg 55 arcmin 05 arcsec (1950) and contains two candidate stars of approximately 20th magnitude. No coincident point source of radio emission is known, but it is pointed out that the X-ray object lies 1.2 deg away from the centroid position of a gamma-ray source, CG 333 + 0. The observed flux from the object at the earth is approximately 7 x 10 to the -13th ergs/sq cm s in the 0.6-2 keV band. It is likely that the object is either a hot neutron star or an X-ray emitting pulsar. In contrast to the Crab and Vela pulsars, however, no extended X-ray emission associated with the point source is discernible. If the object is a hot neutron star, it has a blackbody temperature of 2 x 10 to the 6th K, and would represent the first detection of surface radiation from a neutron star.

Tuohy, I.↗
NASA NTRS1979

Observations of particle acceleration in solar flares

Solar flares provide several examples of nonthermal particle acceleration. The paper reviews the information gained about these processes via X-ray and gamma-ray astronomy, which can presently distinguish among three separate particle-acceleration processes at the sun: an impulsive accelerator of more than 20 keV electrons, a gradual accelerator of more than 20 keV electrons, and a gradual accelerator of more than 10 MeV ions. The acceleration energy efficiency (total particle energy divided by total flare energy) of any of these mechanisms cannot be less than about 0.1%, although the gradual acceleration does not occur in every flare. The observational material suggests that both the impulsive and gradual accelerations take place preferentially in closed magnetic-field structures, but that the electrons decay in these traps before they can escape. The ions escape very efficiently.

Hudson, H. S.↗
NASA NTRS1979

Energetic particles in solar flares

The principal properties of energetic particles accelerated in solar flares are reviewed. Particular emphasis is placed on the high-energy flare component whose acceleration is often referred to as second-phase acceleration. Stochastic Fermi acceleration is treated analytically, and the results of the computation are compared with particle and gamma-ray data to deduce information on the timing of the acceleration, the spectrum of the particles, and the energy content of the nucleonic component. A discussion of He-3 and heavy element abundances is also presented.

Ramaty, R.↗
NASA NTRS1981

Grand unification and possible matter-antimatter domain structure in the universe

The theory and basic concepts for the development of a matter-antimatter domain cosmology are outlined within the framework of the grand unified gauge theory paradigm. It is shown how spontaneous CP symmetry breaking leads to such a domain sturcture in the universe. Astrophysical data such as the cosmic gamma-ray background spectrum, cosmic-ray p flux measurements, and galaxy clustering are found to favor this point of view. Future tests of this form of big-bang cosmology are suggested and discussed, including tests using deep underwater cosmic ray neutrino detectors.

Stecker, F. W.↗
NASA NTRS1981

Solar flare observations and their interpretations

A solar flare has a characteristic spatial extent of 10,000 to 100,000 km. It develops rapidly, with a characteristic time scale of 100 to 1000 s but its manifestations can be observed for hours after onset. A solar flare is the source of highly energetic particles with energies that extend into the GeV range; it produces copious amounts of electromagnetic radiation from gamma-rays to wavelengths of 10 km; and it produces violent magnetohydrodynamic phenomena such as shocks and fast mass ejections. The three basic phases of a flare are described and are: the precursor (preflare) phase, lasting for minutes to hours; the flash phase, lasting for 1 to 5 minutes; and the main (gradual) phase, lasting, on occasion, for hours.

Brown, J. C.↗
NASA NTRS1980

The energy loss of relativistic electrons in energetic photon gases and its relation to the equilibrium spectrum of electrons

The energy loss of relativistic electrons is considered for astrophysical objects which contain energetic photon gases in the XUV-range. Such objects have been suggested as possible candidates for gamma-ray point sources through the mechanism of inverse Compton scattering. In certain cases where inverse Compton scattering is the dominant energy loss mechanism, an equilibrium spectrum results which can deviate from a strict power law. Such an effect can have consequences on the observed radiation spectrum from such objects.

Prince, T.↗
NASA NTRS1980

Galactic and extragalactic high energy neutrinos

Estimates of fluxes from cosmic diffuse sources are made using the generic relationship between secondary gammas and neutrinos and using recent cosmic gamma-ray satellite observations. A quantitative estimate of the observability above the atmospheric background of 1-10 TeV neutrinos from the inner Galaxy for a DUMAND type detector is then given.

Stecker, F. W.↗
NASA NTRS1980

HEAO - Signature of a successful space science program

The HEAO (High Energy Astronomy Observatory) Program consists of three large automated scientific observatories launched between 1977 and 1979 to observe from near-earth orbit stellar X-ray and gamma-ray sources and to measure incoming cosmic ray particles. The HEAO-2 and HEAO-3 spacecraft are expected to exceed their design lifetimes by a factor of three, as did HEAO-1, which operated for 18 months. All three missions are considered successful in that target dates have essentially been met, launch and flight operations have been relatively smooth, instrumentation has performed well, and there have been no cost overruns. The paper lists ten factors contributing to the missions' success, among them a thorough definition before program start, commonality of spacecraft design, redundancy of mission critical equipment, ample design margins, and tight control of system changes. Specific mission parameters are included in the paper as well as the technological advances engendered by the HEAO Program in such areas as high-resolution X-ray optics and solid-state spectrometry.

Speer, F. A.↗
NASA NTRS1981

Radiation damage of the HEAO C-1 germanium detectors

The effects of radiation damage from proton bombardment of the four HEAO C-1 high purity germanium detectors have been measured and compared to predictions. Because of the presence of numerous gamma-ray lines in the detector background spectra and because of the relatively long exposure time of the HEAO 3 satellite to cosmic-ray and trapped protons, it has been possible to measure both the energy and time dependence of radiation damage. After 100 d in orbit, each of the four detectors has been exposed to approximately 3 x 10 to the 7th protons/sq cm, and the average energy resolution at 1460 keV had degraded from 3.2 keV fwhm to 8.6 keV fwhm. The lines were all broadened to the low energy side although the line profile was different for each of the four detectors. The damage-related contribution to the degradation in energy resolution was found to be linear in energy and proton influence.

Mahoney, W. A.↗
NASA NTRS1980

Nuclear gamma rays from 720-MeV alpha-induced reactions on Al-27 and Si-28

Prompt gamma rays from the interaction of 720-MeV alpha particles with Al-27 and Si-28 were detected and analyzed to identify residual nuclei and to determine cross sections for production of specific levels. No gamma-ray transitions were detected from nuclei heavier than the target. From Doppler broadening, the momentum of the residual nuclei was estimated. The results are compared with previous results for 140- and 1600-MeV alphas on Al-27 and approximately 200-MeV positive or negative pions on Al-27 and Si-28 and fitted to a spallation-yield formula.

Lieb, B. J.↗
NASA NTRS1981

HEAO 3 measurements of the atmospheric positron annihilation line

The atmospheric positron annihilation line at 511 keV was the first gamma-ray line observed which originates from processes of astrophysical importance. Measurements of the properties of a positron annihilation line make it possible to determine many of the physical conditions present at the source of emission. An investigation was conducted of the 511-keV line measured with the HEAO C-1 experiment. The HEAO C-1 experiment consisted of a cluster of four, large, high-purity germanium detectors surrounded by an active anticoincidence CsI shield. A strong atmospheric line was measured at 511.07 + or - 0.10 keV. The net atmospheric emission has been accurately determined as a function of geomagnetic latitude and varies from 0.01 photons/sq cm-sec-sr near the magnetic equator to 0.035 photons/sq cm-sec-sr at a latitude of 55 deg.

Mahoney, W. A.↗
NASA NTRS1980

Enhanced orbital geochemical images by the Laplacian subtraction method

Orbital geochemical studies of the moon based on X-ray fluorescence and gamma-ray spectroscopy have been successful. There are, however, difficulties if geologic units or other features to be investigated are too small. Investigations have been conducted with the objective to improve with the aid of image enhancement methods both spatial resolution and contrast for the geochemical experiments. A description is provided of the Laplacian subtraction method of enhancement. It was found that the application of a least-squares version of this method to the Mg/Al ratios obtained by orbital X-ray fluorescence improved geochemical images considerably. The spatial resolution increased by about a factor of 2 and the contrast also increased. The Laplacian of an image can also be used to detect very small 'hot' or 'cold' spots in an image.

Schonfeld, E.↗
NASA NTRS1988

Supernova 1987A

Supernova 1987A (February 23, 1987) in the Large Magellanic Cloud is the brightest supernova to be observed since SN 1604 AD (Kepler). Detection of a burst of neutrinos indicates that a neutron star was formed. Radioactive decay of about 0.07 solar mass of Co-56 is responsible for the observed optical light as well as hard X-rays and gamma-ray lines. Ultraviolet, optical, and infrared 'light echoes' and soft X-rays provide information on the distribution of circumstellar matter and the evolution of the progenitor star.

Mccray, Richard↗
NASA NTRS1971

Neutron Activation Analysis of Water - A Review

Recent developments in this field are emphasized. After a brief review of basic principles, topics discussed include sources of neutrons, pre-irradiation physical and chemical treatment of samples, neutron capture and gamma-ray analysis, and selected applications. Applications of neutron activation analysis of water have increased rapidly within the last few years and may be expected to increase in the future.

Buchanan, John D.↗