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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 217 records · Page 12
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NASA NTRS1976

Neutral-atom electron binding energies from relaxed-orbital relativistic Hartree-Fock-Slater calculations for Z between 2 and 106

Electron binding energies in neutral atoms have been calculated relativistically, with the requirement of complete relaxation. Hartree-Fock-Slater wave functions served as zeroth-order eigenfunctions to compute the expectation of the total Hamiltonian. A first-order correction to the local approximation was thus included. Quantum-electrodynamic corrections were made. For all elements with atomic numbers ranging from 2 to 106, the following quantities are listed: total energies, electron kinetic energies, electron-nucleus potential energies, electron-electron potential energies consisting of electrostatic and Breit interaction (magnetic and retardation) terms, and vacuum polarization energies. Binding energies including relaxation are listed for all electrons in all atoms over the indicated range of atomic numbers. A self-energy correction is included for the 1s, 2s, and 2p(1/2) levels. Results for selected atoms are compared with energies calculated by other methods and with experimental values.

Huang, K.-N.↗
NASA NTRS2020

Plasma environment effects on K lines of astrophysical interest IV. IPs, K thresholds, radiative rates, and Auger widths in Fe ii–Fe viii

Aims. Within the framework of compact-object accretion disks, we calculate plasma environment e ects on the atomic structure and decay parameters used in the modeling of K lines in lowly charged iron ions, namely Fe ii–Fe viii. Methods. For this study, we used the fully relativistic multiconfiguration Dirac–Fock method approximating the plasma electron–nucleus and electron-electron screenings with a time-averaged Debye-Hückel potential. Results. We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges 10(exp 5)-10(exp 7) K and 10(exp 18)-10(exp 22) per cu.cm. In addition, we propose two universal fitting formulae to predict the IP and K-threshold lowerings in any elemental ion. Conclusions. We conclude that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be able to detect the lowering of the K edges of these Fe ions due to the extreme plasma conditions occurring in the accretion disks around compact objects.

J. Deprince↗
NASA NTRS1973

Determination of the relativistic time delay for Mariner 9: A status report on the JPL analysis of normal points

The procedure which has been chosen to accomplish a reduction of the Mariner 9 tracking data makes use of Doppler data over relatively short arcs of about one to nine orbital revolutions to determine the orbit of the spacecraft about Mars. Next, with the knowledge of the Mars-centered orbit, it is possible to use the range data to the spacecraft to determine the distance between the center of earth and the center of Mars for each short interval of tracking data. These reduced range measurements between the centers of the two planets make up the basic data for the relativity test.

Anderson, J. D.↗
NASA NTRS2007

Effect of EMIC Wave Normal Angle Distribution on Relativistic Electron Scattering in Outer RB

We present the equatorial and bounce average pitch angle diffusion coefficients for scattering of relativistic electrons by the H+ mode of EMIC waves. Both the model (prescribed) and self consistent distributions over the wave normal angle are considered. The main results of our calculation can be summarized as follows: First, in comparison with field aligned waves, the intermediate and highly oblique waves reduce the pitch angle range subject to diffusion, and strongly suppress the scattering rate for low energy electrons (E less than 2 MeV). Second, for electron energies greater than 5 MeV, the |n| = 1 resonances operate only in a narrow region at large pitch-angles, and despite their greatest contribution in case of field aligned waves, cannot cause electron diffusion into the loss cone. For those energies, oblique waves at |n| greater than 1 resonances are more effective, extending the range of pitch angle diffusion down to the loss cone boundary, and increasing diffusion at small pitch angles by orders of magnitude.

Khazanov, G. V.↗
NASA NTRS2011

Planck Early Results. XV. Spectral Energy Distributions and Radio Continuum Spectra of Northern Extragalactic Radio Sources

Spectral energy distributions (SEDs) and radio continuum spectra are presented for a northern sample of 104 extragalactic radio sources. based on the Planck Early Release Compact Source Catalogue (ERCSC) and simultaneous multi frequency data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous observations ranging from radio to gamma-rays. This is the first extensive frequency coverage in the radio and millimetre domains for an essentially complete sample of extragalactic radio sources, and it shows how the individual shocks, each in their own phase of development, shape the radio spectra as they move in the relativistic jet. The SEDs presented in this paper were fitted with second and third degree polynomials to estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and the spectral indices of low and high frequency radio data, including the Planck ERCSC data, were calculated. SED modelling methods are discussed, with an emphasis on proper. physical modelling of the synchrotron bump using multiple components. Planck ERCSC data also suggest that the original accelerated electron energy spectrum could be much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The implications of this are discussed for the acceleration mechanisms effective in blazar shock. Furthermore in many cases the Planck data indicate that gamma-ray emission must originate in the same shocks that produce the radio emission.

Aatrokoski, J.↗
NASA NTRS2019

EMIC Wave-Driven Bounce Resonance Scattering of Energetic Electrons in the Inner Magnetosphere

While electromagnetic ion cyclotron (EMIC) waves have been long studied as a scattering mechanism for ultrarelativistic (megaelectron volt) electrons via cyclotron‐resonant interactions, these waves are also of the right frequency to resonate with the bounce motion of lower‐energy (approximately tens to hundreds of kiloelectron volts) electrons. Here we investigate the effectiveness of this bounce resonance interaction to better determine the effects of EMIC waves on subrelativistic electron populations in Earth's inner magnetosphere. Using wave and plasma parameters directly measured by the Van Allen Probes, we estimate bounce resonance diffusion coefficients for four different events, illustrative of wave and plasma parameters to be encountered in the inner magnetosphere. The range of electron energies and pitch angles affected is examined to better assess the realistic effects of EMIC‐driven bounce resonance on energetic electron populations based on actual, locally observed event‐based parameters. Significant local diffusion coefficients (~ > 10(exp −6) s(exp −1)) for 50‐ to 100‐keV electrons are achieved for both H+ band wave events as well as He+ band, with diffusion coefficients peaking for near‐90° pitch angles but remaining elevated for intermediate ones as well. Diffusion coefficients for higher‐energy 200‐keV electrons are typically multiple orders of magnitude lower (ranging from 10(exp −11) to 10(exp −6) s(exp −1)) and often peak at lower pitch angles (~20–30°). These results suggest that both H+ and He+ band EMIC waves can play a role in shaping lower‐energy electron dynamics via bounce‐resonant interactions, in addition to their role in relativistic electron loss via cyclotron resonance.

Blum, L. W.↗
NASA NTRS1983

Local superbubble model of cosmic ray propagation

The consequences for cosmic ray phenomena of the solar system being inside a superbubble are explored. The superbubble is found to expand with time, thus causing the contained relativistic cosmic rays to lose energy. The local superbubble model offers a natural explanation for features in the high energy cosmic ray anisotropy and spectrum which occur around 10 to the 15th eV and which are due to failure of the superbubble wall to contain cosmic rays of high energy. In the energy range from 3 x 10 to the 14th eV to 10 to the 17th eV, the direction of the measured anisotropy indicates a net local flow from the nearby wall, whereas above 10 to the 17th eV the anisotropy direction is reversed, indicating a return to net outward flow of cosmic rays toward the local wall.

Streitmatter, R. E.↗
NASA NTRS1999

Optical Variability of Blazars

In this paper we show the results of our monitoring the flux variability of 15 blazars, within the redshift range of 0.07 to 2.06, all with a visual magnitude range between 14 and 20 mag. Because blazars have displayed variability on diverse timescales, we have chosen to study them over both short and long timescales, ranging from minutes to years. These blazars were observed on 58 nights between March 1995 and June 1998. Individual sources are discussed in detail. For example, one of our sources, Mkn5Ol showed microvariability of as much as 0.13 mag change within 12 minutes. The usual parameters for size, mass, and luminosity are calculated. Relativistic beaming is implied by the data. We also searched for correlations between amplitude of variability, redshift, and luminosity. We found few if any such correlations. Discussion and conclusions are given for these and other results as implied by the data.

Ghosh, K. K.↗
NASA NTRS2015

1FGL J1417.7-4407: A Likely Gamma-Ray Bright Binary with A Massive Neutron Star and A Giant Secondary

We present multiwavelength observations of the persistent Fermi-Large Area Telescope unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 solar mass) and a approximately 0.35 solar mass giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk-magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma- ray to X-ray luminosity (approximately 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.

binaries: spectroscopic aEuro" gamma rays: general↗
NASA NTRS1982

Atomic clocks for astrophysical measurements

It is noted that recently developed atomic hydrogen masers have achieved stability well into the 10 to the -16th domain for averaging time intervals beyond 1000 sec and that further improvements are in prospect. These devices are highly adaptable for space use in very high precision measurements of angle through Very Long Baseline Interferometry (VLBI) and of range and range-rate through Doppler techniques. Space missions that will use these clocks for measuring the sun's gravity field distribution and for testing gravitation and relativity (a project that will include a search for pulsed low-frequency gravitational waves) are discussed. Estimates are made of system performance capability, and the accuracy capability of relativistic measurements is evaluated in terms of the results from the 1976 NASA/SAO spaceborne clock test of the Einstein Equivalence Principle.

Vessot, R. F. C.↗
NASA NTRS1988

Multiple nucleon knockout by Coulomb dissociation in relativistic heavy-ion collisions

The Coulomb dissociation contributions to fragmentation cross sections in relativistic heavy ion collisions, where more than one nucleon is removed, are estimated using the Weizsacker-Williams method of virtual quanta. Photonuclear cross sections taken from experimental results were used to fold into target photon number spectra calculated with the Weizsacker-Williams method. Calculations for several projectile target combinations over a wide range of charge numbers, and a wide range of incident projectile energies, are reported. These results suggest that multiple nucleon knockout by the Coulomb field may be of negligible importance in galactic heavy ion studies for projectiles lighter than Fe-56.

Cucinotta, Francis A.↗
NASA NTRS1994

EGRET upper limits to the high-energy gamma-ray emission from the millisecond pulsars in nearby globular clusters

We report upper limits to the high-energy gamma-ray emission from the millisecond pulsars (MSPs) in a number of globular clusters. The observations were done as part of an all-sky survey by the energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) during Phase I of the CGRO mission (1991 June to 1992 November). Several theoretical models suggest that MSPs may be sources of high-energy gamma radiation emitted either as primary radiation from the pulsar magnetosphere or as secondary radiation generated by conversion into photons of a substantial part of the relativistic e(+/-) pair wind expected to flow from the pulsar. To date, no high-energy emission has been detected from an individual MSP. However, a large number of MSPs are expected in globular cluster cores where the formation rate of accreting binary systems is high. Model predictions of the total number of pulsars range in the hundreds for some clusters. These expectations have been reinforced by recent discoveries of a substantial number of radio MSPs in several clusters; for example, 11 have been found in 47 Tucanae (Manchester et al.). The EGRET observations have been used to obtain upper limits for the efficiency eta of conversion of MSP spin-down power into hard gamma rays. The upper limits are also compared with the gamma-ray fluxes predicted from theoretical models of pulsar wind emission (Tavani). The EGRET limits put significant constraints on either the emission models or the number of pulsars in the globular clusters.

Michelson, P. F.↗
NASA NTRS1994

Multiwavelength Search for Correlated Time Variations in the Brightest EGRET Blazars

We have found that the emission in the blazar jets is highly stratified, as evidenced by time delays between the peaks of the flares at different wavebands. This fits well with the predictions of the jet models. Not all of the blazars have yet been observed long enough with the VLBA to determine the motions of their components. However, for those 39 blazars for which this analysis is possible as of August 1997, the apparent superluminal speeds are very high, ranging from about 10 to 35c (for a Hubble constant of 65 km/s Mpc. If this trend holds for the remainder of the sample (to be determined after the results of observations in July 1997 are analyzed along with those from previous epochs), the implication is that the EGRET-detected blazars have stronger relativistic beaming than does the general radio-bright blazar population.

Marscher, Alan P.↗
NASA NTRS2000

Optical Variability of Blazars

In this paper we show the results of our monitoring the flux variability of 15 blazars, within the redshift range of 0.07 - 2.06, all with a visual magnitude range between 14 and 20 mag. Because blazars have displayed variability on diverse timescales, we have chosen to study them over both short and long timescales, ranging from minutes to years. These blazars were observed on 58 nights between 1995 March and 1998 June. Individual sources are discussed in detail. For example, one of our sources, Mrk 501, showed microvariability of as much as 0.13 mag change within 12 minutes. The usual parameters for size, mass, and luminosity are calculated. Relativistic beaming is implied by the data. We also searched for correlations between amplitude of variability, redshift, and luminosity. We found few, if any, such correlations. Discussion and conclusions are given for these and other results as implied by the data.

Ghosh, K. K.↗
NASA NTRS2005

Solar-System Tests of Gravitational Theories

We are engaged in testing gravitational theory, mainly using observations of objects in the solar system and mainly on the interplanetary scale. Our goal is either to detect departures from the standard model (general relativity) - if any exist within the level of sensitivity of our data - or to support this model by placing tighter bounds on any departure from it. For this project, we have analyzed a combination of observational data with our model of the solar system, including planetary radar ranging, lunar laser ranging, and spacecraft tracking, as well as pulsar timing and pulsar VLBI measurements. In the past year, we have added to our data, primarily lunar laser ranging measurements, but also supplementary data concerning the physical properties of solar-system objects, such as the solar quadrupole moment, planetary masses, and asteroid radii. Because the solar quadrupole moment contributes to the classical precession of planetary perihelia, but with a dependence on distance from the Sun that differs from that of the relativistic precession, it is possible to estimate effects simultaneously. However, our interest is mainly in the relativistic effect, and we find that imposing a constraint on the quadrupole moment from helioseismology studies, gives us a dramatic (about ten-fold) decrease in the standard error of our estimate of the relativistic component of the perihelion advance.

Shapiro, Irwin I.↗
NASA NTRS1985

A simulation study of kilometric radiation generation along an auroral field line

A model for the high-altitude auroral zone is combined with local particle simulations in order to assess the quantitative implications of relativistic dispersion for the generation of auroral kilometric radiation. The auroral zone model is described, including the distribution functions for the primary and secondary electron populations and the variations of the total number density with altitude. The analysis shows that the most intense cyclotron maser emission should occur in the 1.75-2.0 R(E) altitude range. At lower altitudes, the secondary electrons are dominant, and the instability saturates at a low level. At higher altitudes, the energy of the primary electron is lower, and again the radiation level drops. The simulations indicate that linear growth rates of the order of 0.002 Omega(e) occur in this region and that the conversion of primary electron energy into AKR is about one percent.

Pritchett, P. L.↗
NASA NTRS1985

Improved excitation rate coefficients for the n = 2 and n = 3 levels of Ca XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).

Pradhan, A. K.↗