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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Higher order Compton-Getting anisotropies.

The Compton-Getting effect relates the distribution function of a particle population in a given frame of reference to that in another frame, moving at constant velocity V relative to the first. A study is made of the effects that arise when, contrary to previous assumptions, second-order terms in (V/v), where v is the particle velocity, are retained, and when the given distribution function is not isotropic. The importance of the extra terms is then examined in the specific case of low-energy solar protons in interplanetary space.

Balogh, A.↗
NASA NTRS1980

A galactic component of the diffuse X-ray flux in the range 2-7 keV

An analysis of the spatial distribution of the 2-7 keV X-ray background measured by Uhuru and reported by Schwartz (1979) is presented. The latitude distribution above 10 deg is consistent with a uniform isotropic component comprising the bulk of the radiation plus a galactic part varying from 3% at /b/ = 20 deg to 1% at /b/ = 90 deg. An analysis was made of the residual background based on the work of Warwick, Pye, and Fabian, in terms of a directional anisotropy as indicated by the Compton-Getting effect; the symmetrical galactic contribution was subtracted in the computations. It was shown that the results are consistent with the solar system moving through the 2-7 keV X-ray sea in the same manner as it appears to move with respect to the 2.7 K radiation.

Protheroe, R. J.↗
NASA NTRS1981

Compton losses, Compton rockets

The radiation force on a relativistic plasma is shown to accelerate the plasma to relativistic bulk velocities under certain conditions, thus demonstrating that relativistic bulk motion not only alleviates Compton losses, but can also result from such losses. In order to isolate Compton-rocket effects from hydrodynamical ones, it is assumed that the plasma in its instantaneous rest frame has a temporally constant density and is spatially uniform.

Cheng, A. Y. S.↗
NASA NTRS1989

The Gamma-Ray Observatory

The scientific goals and the design of the NASA Gamma-Ray Observatory (GRO), planned for launch in mid-1990, are described together with the experiments to be performed on the GRO mission and the instruments to be flown on the Observatory. GRO contains a complement of four instruments to span the spectrum from 0.03 to 20,000 MeV in energy, three of which are optimized to make gamma-ray observations using either the photoelectric effect, the Compton scatter, or the pair production processes; the fourth instrument is optimized for high-sensitivity observations of transient events and time-variable sources. The instruments are the Oriented Scintillation Spectrometer Experiment, the Compton Telescope, the Energetic Gamma-Ray Experiment Telescope, and the Burst and Transient Source Experiment.

Kniffen, Donald A.↗
NASA NTRS1992

Time-dependent models of magnetized pair plasmas

Attention is given to a numerical code developed to study the time evolution of electron-positron plasmas. The code solves in a self-consistent manner kinetic equations describing the effects of Compton scattering, two-photon pair production, pair annihilation, cooling of pairs via Coulomb scattering, e-e bremsstrahlung, and synchrotron radiation. The kinetic equations are derived under the approximation of homogeneous and isotropic particle distributions on the basis of a study by Coppi and Blandford (1993). Both stationary and time-varying output radiation spectra are computed. Good qualitative agreement with previous calculations is found, except where the differences are attributable to the improved treatment of the microphysics.

Coppi, Paolo S.↗
NASA NTRS1995

Astro-1 and ground-based observations of Markarian 335: Evidence for an accretion disk

Simultaneous UV and optical observations of the Seyfert galaxy Markarian 335 (z = 0.026) during the Astro-1 mission yield a spectrum spanning the wavelength range of 912-8410 A. In the sub-Ly alpha region a prominent blended emission feature of O VI lambda lambda 1032, 1038, and Ly beta is nearly as strong as C IV wavelength 1549. The continuum flux extends beyond the redshifted Luman limit without a noticeable discontinuity, but a siginificant change in slope exists near the redhsifted Lyman edge. We suggest that such a change may be the signature of a Lyman edge in an accretion disk seen at a small inclination angle. Using a disk model including such an edge, we fit the spectrum with a central black hole mass of 5 x 10(exp 7) solar mass, an accretion rate of 0.07 solar mass/yr, and an optical depth at the Lyman edge of 0.4. To account for the strong O VI emission as well as the soft X-ray excess, we consider the effects of Comptonization on the disk spectrum, which can produce a high-energy tail for the UV bump and also smooth the Lyman edge feature.

Zheng, W.↗
NASA NTRS1996

The Compton Mirror in NGC 4151

We show that the sharp cutoff in the hard X-ray spectrum of NGC 4151, unusual for Seyfert 1 galaxies, can be reconciled with the average Seyfert 1 spectrum if we assume that the central source is completely hidden from our line of sight by the thick part of the accretion disk or by the broad emission-line clouds. The observed X-ray radiation is produced by scattering of the Seyfert 1 type spectrum in the higher, cooler parts of the accretion disk corona, or in a wind. A sharp cutoff appears as a result of the Compton recoil effect. This model naturally explains a discrepancy regarding the inclination of the central source, inferred to be low (face-on) from observations of the iron K-alpha emission line, but inferred to be high on the basis of optical and UV observations.

Poutanen, Juri↗
NASA NTRS2016

Distance to the IBEX Ribbon Source Inferred From Parallax

Maps of energetic neutral atom (ENA) fluxes obtained from observations made by the Interstellar Boundary Explorer (IBEX) revealed a bright structure extending over the sky, subsequently dubbed the IBEX ribbon. The ribbon had not been expected from the existing models and theories prior to IBEX, and a number of mechanisms have since been proposed to explain the observations. In these mechanisms, the observed ENAs emerge from source plasmas located at different distances from the Sun. Since each part of the sky is observed by ibex TWICE DURING THE YEAR FROM OPPOSTIE SIDE OF THE Sun, the apparent position of the ribbon as observed in the sky is shifted due to parallax. To determine the ribbons parallax, we found the precise location of the maximum signal of the ribbon observed in each orbital arc. The apparent positions obtained were subsequently corrected for the Compton-Getting effect, gravitational deflection, and radiation pressure. Finally, we selected a part of the ribbon where its position is similar in the different IBEX ENERGY PASSBANDS. We compared the apparent positions obtained from the viewing locations on the opposite sides of the Sun, and found that they are shifted by a parallax angle of 0 41 0 15, which corresponds to a distance of AU. This finding supports models of the ribbon with the source located just outside the heliopause.

ISM: atoms↗
NASA NTRS1991

Tables of model atmospheres of bursting neutron stars

This paper presents tables of plane-parallel neutron star model atmospheres in radiative and hydrostatic equilibrium, with effective temperatures of 8 x 10 exp 6, 1.257 x 10 exp 7, 2 x 10 exp 7, and 3 x 10 exp 7 K, and surface gravities of 15.0 and less (cgs units). The equations of model atmospheres on which the tables are based fully account for nonisotropies of the radiation field and effects of noncoherent Compton scattering of thermal X-rays by free electrons. Both the effective temperatures and gravities listed above are measured on the neutron star surface.

Madej, Jerzy↗
NASA NTRS1994

Relativistic induced Compton scattering in synchrotron self-absorbed sources

We present a model of the radio emission from synchrotron self-absorbed sources, including the effects of induced Compton scattering by the relativistic electrons in the source. Order of magnitude estimates show that stimulated scattering becomes the dominant absorption process when (kT(sub B)/m(sub e) c(exp 2))Tau(sub T) greater than or approximately 1.0. Numerical simulations demonstrate that relativistic induced Compton scattering limits the brightness temperature of a self-absorbed synchroton sources to T(sub B) less than or approximately 2 x 10(exp 11) nu(exp -1/p + 3) (sub zero, 9) gamma(exp p + 2/p + 5) (sub min) K, where gamma(sub min) is the low-energy cutoff to the relativistic electron distribution with a power-law index of p. It can also significantly flatten the radio spectrum. The radio spectrum of the core of 3C 279 is well matched by a model in which stimulated scattering is important, and the additional constraint T(sub B) less than 2 x 10(exp 11)K may be important to the interpretation of the broadband spectra in variable extragalactic compact radio sources. Stimulated scattering reduces the amplitude of the radio frequency variability relative to the X-ray variability, an effect which can be detected by multiwavelength variability studies. Data for a sample of resolved compact radio cores indicate that it is inconsistent to neglect induced Compton scattering when inferring the physical parameters of the sources. The necessary generalizations to the standard synchrotron self-Compton theory are p resented.

Sincell, Mark W.↗
NASA NTRS2002

Regimes of Pulsar Pair Formation and Particle Energetics

We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.

Harding, Alice K.↗
NASA NTRS1979

Spectral formation in compact X-ray sources

A method is described for calculating the transfer of X-rays through gas that is optically thick to Compton scattering. The method permits the simultaneous solution of the radiation-dominated temperature and ionization structure of the medium as well as the effects of incoherent Compton scattering of photons. Self-consistent results are obtained for idealized models of compact X-ray sources, represented as point sources of continuum X-rays surrounded by spherical shells of gas, demonstrating the range of spectral features that might result from such optically thick transfer. Some implications for the analysis of X-ray spectra of galactic X-ray sources are discussed.

Ross, R. R.↗