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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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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

Pulsar gamma-rays: Spectra luminosities and efficiencies

The general characteristics of pulsar gamma ray spectra are presented for a model where the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. The shape of the spectrum is found to depend on pulsar period, magnetic field strength, and primary particle energy. By a comparison of numerically calculated spectra with the observed spectra of the Crab and Vela pulsars, it is determined that primary particles must be accelerated to energies of about 3 x 10 to the 7th power mc sq. A genaral formula for pulsar gamma ray luminosity is determined and is found to depend on period and field strength.

Harding, A. K.↗
NASA NTRS1981

Galactic X-ray emission from pulsars

The contribution of pulsars to the gamma-ray flux from the galactic plane is examined using data from the most recent pulsar surveys. It is assumed that pulsar gamma-rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. Assuming that all pulsars produce gamma-rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. Using the distribution of pulsars in the galaxy as determined from data on 328 pulsars detected in three surveys, the local gamma-ray production spectrum, the longitude profile, and the latitude profile of pulsar gamma-ray flux are calculated. The largest sources of uncertainty in the size of the pulsar contribution are the value of the mean interstellar electron density, the turnover in the pulsar radio luminosity function, and the average pulsar magnetic field strength. A present estimate is that pulsars contribute from 15 to 20 % of the total flux of gamma-rays from the galactic plane.

Harding, A. K.↗
NASA NTRS1981

Pulsar gamma-rays - Spectra, luminosities, and efficiencies

The general characteristics of pulsar gamma-ray spectra are presented for a model in which the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. It is found that the shape of the spectrum depends on pulsar period, magnetic field strength, and primary particle energy. Comparing numerically calculated spectra with the observed spectra of the Crab and Vela pulsars, it is determined that primary particles must be accelerated to energies of approximately 3 x 10 to the 7th m c-squared. A general formula is determined for pulsar gamma-ray luminosity; it is found to depend on period and field strength.

Harding, A. K.↗
NASA NTRS1981

Galactic gamma-ray emission from pulsars

Using data from the most recent pulsar surveys, the contribution of pulsars to the gamma-ray flux from the galactic plane is examined. The assumption is made that pulsar gamma rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. If the assumption is made that all pulsars produce gamma rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. The distribution of pulsars in the Galaxy is determined using data on 328 pulsars detected in three surveys. The Z and R distributions are found to be very sensitive to the mean electron density in the galactic plane, as are the total number and birthrate of pulsars in the Galaxy. Longitude profile of pulsar gamma-ray flux are calculated for different values of the mean electron density.

Harding, A. K.↗
NASA NTRS1981

Detectors for energies less than 10 MeV

In the energy domain 100 keV to 10 MeV, both crystal scintillations and semiconductors are widely used for gamma ray detectors in spectrometer systems. These detectors' operation depend on the fact that gamma rays lose energy by ionization in these materials and electrons and holes are produced. In the case of semiconductors, these electrons and holes are collected by an electric field, and they provide an electric signal that is a direct measure of the energy lost by the gamma ray in the material. Scintillation detectors depend on a further conversion of the energy lost in electron hole pair production to the production of photons. A photomultiplier tube measures the intensity of the photon flux, and an electrical pulse proportional to the photon intensity is produced at the photomultiplier output.

Source record↗
NASA NTRS1981

Double Compton scatter telescope calibration

Calibration techniques for a medium energy gamma ray telescope are described. Gain calibration using Compton edge spectra involves comparisons of pulse height spectra with spectra simulated by a Monte Carlo computer code which includes Compton scattering and pair production, plural scattering and variable energy resolution, and cell size. The telescope considered comprises 56 cells of liquid scintillator in four size groups, with a total liquid volume of 325 l; each cell has its own photomultiplier tube. Energy and angular resolutions and the PMT gain calibration procedure are verified with double scatter data for monoenergetic gamma rays at a known location. Detection probabilities for any cell combination in the two telescope arrays are calculated per steradian as a function of the scattering for a number of different energies with a Van de Graaff accelerator.

Dayton, B.↗
NASA NTRS1982

Physical processes in gamma-ray bursts

Physical processes occurring in gamma-ray bursts are discussed, with special attention to the event of March 5, 1979 in the Large Magellanic Cloud. The source of that event's extraordinary intense line and continuum radiation has been explained as a pair plasma confined in a strong magnetic field, as in a neutron star magnetosphere, and some consequences of that model are studied. The magnetic field (approximately 10 to the 13th gauss) affects both plasma physical processes and annihilation, so that accurate measurements of the annihilation line shape may lead to quantitative field determinations. A simple model for gamma-gamma pair production and annihilation is calculated, implying that this process will not prevent escape of intense gamma-ray fluxes. Finally, energetic considerations suggest that the magnetospheric energy may be regenerated from internal sources, either during or between bursts.

Katz, J. I.↗
NASA NTRS1983

Active galaxies and the diffuse Gamma-Ray background

A model for the origin of relativistic particles and gamma rays in active galactic nuclei and quasars, together with recent HEAO-1 observations of the spectra of active galaxies from 2 to 165 keV, provide the basis for a reexamination of the nature of the extragalactic gamma ray background. Active galaxies account for the observed background if their X-ray spectra steepen to E.021 above 100 keV, as observed in Cen-A, together with a further steepening to E.021 as a result of absorption of gamma rays by photon-photon pair production interactions with X-ray photons. The compactness of active galaxies required to give this steepening is consistent with estimates of their typical luminosity and radius.

Kazanas, D.↗
NASA NTRS1982

Relativistic plasmas

Recent work on the kinetic theory of a highly relativistic electron gas and the associated photon opacity is discussed. The relaxation time for thermalization by Moller scattering is compared with the characteristic times associated with various loss processes acting to perturb the distribution away from equilibrium. For an optically thin plasma, bremsstrahlung is found to dominate Moller scattering when the dimensionless electron temperature is greater than about 3.5. Results are presented for the opacity from Compton scattering, pair production in the fields of electrons and ions, inverse bremsstrahlung, and synchrotron self-absorption.

Gould, R. J.↗
NASA NTRS1983

Active galaxies and the diffuse gamma-ray background

Active galaxies are shown to account for the observed gamma ray background radiation if a steepening of the spectra above about 100 keV is present. An analytical model is discussed in which protons undergo Fermi acceleration at a shock in a spherical accretion flow onto a massive black hole. Relativistic protons with power law spectra, nuclear interactions producing gamma rays from neutal pion decay and electrons from pion-mu meson-electron decay, with a power law spectrum above several hundred MeV, synchrotron and inverse Compton losses steepening the electron spectrum, a photon spectrum close to the pion gamma spectrum and a high-energy gamma ray spectrum steepened by photon-photon pair production interactions with X rays are covered in the model. Comparisons are made with HEAO 2 data on active galaxies, which have estimated luminosities and radii consistent with the compactness necessary for producing the steepening predicted by the model. The active galaxies spectra would be described by a spherical accretion-shock model.

Kazanas, D.↗
NASA NTRS1983

Emission model of gamma-ray bursts

The emission mechanisms of cosmic gamma-ray bursts are reviewed. In particular, the thermal synchrotron model is discussed as the most viable mechanism for the majority of the continuum emission. Within this framework various information about the source region can be extracted. The picture that emerges is that of a hot (kT = .2 - 1.0 sq mc), thin sheet of dense pair-dominated plasma emitting via cyclo-synchrotron radiation in a strong magnetic field (B approximately one-hundred billion to one trillion gauss). Speculations on the origin and structure of this sheet are attempted. The problem of high-energy photons above pair production threshold escaping from the source is also considered.

Liang, E. P.↗
NASA NTRS1983

Galactic absorption of high-energy gamma-rays from Cygnus X-3

The importance of cosmic blackbody photons as an absorbing gas for the attenuation of high-energy photons via pair production in photon-photon collision is examined for the specific case of gamma rays from Cyg X-3. Recent observational results on this photon flux in the range from 2 x 10 to the 15th to 2 x 10 to the 16th eV are corrected for this attenuation. The absorption optical depth to the source is about unity, and the corrected flux is about a factor of three higher; as a result, it does not extrapolate from the data at lower energies (10 to the 12th eV).

Gould, R. J.↗
NASA NTRS1983

Positron-electron annihilation radiation from the Galactic Center

Evidence and arguments are presented supporting the theory that the 0.511 MeV line observed from the Galactic Center stems from photon-photon pair production near a black hole with a mass not greater than approximately 500 solar masses. Observations are reviewed and the subsequent implications on the annihilation site and the positron source are discussed. Because of the variations and line width of the e(+) - e(-) annihilation radiation from the Galactic Center, positrons must essentially be produced by a single source and annihilate in an ambient gas of density greater than 10 to the 5th/cu cm, an ionization fraction greater than 10 percent, a temperature less than 5 x 10 to the 4th K, and be confined to a region of size less than 10 to the 18th cm. Such conditions may exist in warm clouds and other IR sources within the central parsec of the Galaxy.

Ramaty, R.↗
NASA NTRS1984

Power law X- and gamma-ray emission from relativistic thermal plasmas

Pair equilibrium in thermal plasmas emitting power law photon spectra by repeated Compton scatterings of a soft photon source active galactic nuclei was studied. Dependence of the spectral index on optical thickness and on temperature of the plasma is discussed. The equation for pair equilibrium is solved for the maximum steady luminosity. Analytical solutions for the subrelativistic region, and for the ultrarelativistic region are found. In the transrelativistic region the solutions are expressed by single integrals over the pair production cross sections, performed numerically. The constraints on soft photon source imposed by the condition that the soft photon flux cannot exceed the black-body flux are considered. For the Comptonized synchrotron radiation model a relation between magnetic field strength and output luminosity is found.

Zdziarski, A. A.↗
NASA NTRS1985

A simple model of electron beam initiated dielectric breakdown

A steady state model that describes the internal charge distribution of a planar dielectric sample exposed to a uniform electron beam was developed. The model includes the effects of charge deposition and ionization of the beam, separate trap-modulated mobilities for electrons and holes, electron-hole recombination, and pair production by drifting thermal electrons. If the incident beam current is greater than a certain critical value (which depends on sample thickness as well as other sample properties), the steady state solution is non-physical.

Beers, B. L.↗
NASA NTRS1985

The central engine of quasars and AGNs: A relativistic proton radiative shock

Active galactic nuclei (AGNs) and quasars (QSOs) appear to emit roughly equal energy per decade from radio to gamma-ray energies (e.g. Ramaty and Ligenfelter 1982). This argues strongly for a nonthermal radiation mechanism (see Rees 1984). In addition, statistical studies have indicated that the spectra of these objects in the IR-UV and 2 to 50 keV X-ray band, can be fitted very well with power laws of specific indices. These spectral indices do not seem to depend on the luminosity or morphology of the objects (Rothschild et al. 1983; Malkan 1984), and any theory should account for them in a basic and model independent way. If shocks accelerate relativistic protons via the first-order Fermi mechanism (e.g. Axfor 1981), the radiating electrons can be produced as secondaries throughout the source by proton-proton (p-p) collisions and pion decay, thus eliminating Compton losses (Protheroe and Kazanas 1983). As shown by Kazanas (1984), if relativistic electrons are injected at high energies, e+-e- pair production results in a steady state electron distribution that is very similar to that observed in AGNs, independent of the details of injection and the dynamics of the source. The conditions required by this mechanism are met in the shock model of Eichler (1984) and Ellison and Eichler (1984) which allows the self-consistent calculation of the shock acceleration efficiency.

Kazanas, D.↗