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NASA NTRS1990

Observational clues to the energy release process in impulsive solar bursts

The nature of the energy release process that produces impulsive bursts of hard X-rays and microwaves during solar flares is discussed, based on new evidence obtained using the method of Crannell et al. (1978). It is shown that the hard X-ray spectral index gamma is negatively correlated with the microwave peak frequency, suggesting a common source for the microwaves and X-rays. The thermal and nonthermal models are compared. It is found that the most straightforward explanations for burst time behavior are shock-wave particle acceleration in the nonthermal model and thermal conduction fronts in the thermal model.

Batchelor, David↗

NASA NTRS1990

The relationship between energetic particles and flare properties for impulsive solar flares

The impulsive mode of particle acceleration is studied by searching for 0.2-2 MeV electron increases associated with intense type III/V bursts. It is found that the presence of a type III/V burst in association with a relatively intense flare event indicates the acceleration and escape of greater than 100 KeV electrons. A list of type III/V electron events is compiled, showing that the majority included greater than 10 MeV proton increases, although they were not followed by a type II burst. The results suggest that there are two different modes of proton acceleration with the second mode becoming significant only for larger, gradual flares.

Cane, H. V.↗

NASA NTRS1991

Facility Measures Magnetic Fields

Partly automated facility measures and computes steady near magnetic field produced by object. Designed to determine magnetic fields of equipment to be installed on spacecraft including sensitive magnetometers, with view toward application of compensating fields to reduce interfernece with spacecraft-magnetometer readings. Because of its convenient operating features and sensitivity of its measurements, facility serves as prototype for similar facilities devoted to magnetic characterization of medical equipment, magnets for high-energy particle accelerators, and magnetic materials.

Honess, Shawn B.↗

NASA NTRS1991

Study of meteoroid impact craters on various materials (AO 138-1). Attempt at dust debris collection with stacked detectors (AO 138-2)

Part of the Long Duration Exposure Facility (LDEF) tray allocated to French experiments, known as FRECOPA payload, was devoted to the study of dust particles. Two passive experiments were flown: one composed of a set of glass and metallic samples and one composed of multilayer thin foils detectors. In addition to these experiments, a broad variety of materials were exposed to the bombardment of microparticles and provide more data. Thick target experiment comprises selected metallic (Al, Au, Cu, W, Stainless Steel) 250 microns thick and glass surfaces 1.5 mm thick. Crater size distribution from these thick target experiments enable, with the aid of lab calibrations by solid particle accelerators, the evaluation of the incident microparticle flux in the near earth environment. The aim of the multiple foil penetration and collection experiment is primarily to study the feasibility of multilayer thin film detectors acting as energy sorters in order to collect micrometeoroids, if not in their original shape, at least as 'breakup' fragments suitable for chemical analysis. Foil thicknesses range from 0.75 to 5 microns of Al.

Mandeville, Jean Claude↗

NASA NTRS1989

The 1989 NASA-ASEE Summer Faculty Fellowship Program in Aeronautics and Research

The 1989 NASA-ASEE Summer Faculty Fellowship Program at the Goddard Space Flight Center was conducted during 5 Jun. 1989 to 11 Aug. 1989. The research projects were previously assigned. Work summaries are presented for the following topics: optical properties data base; particle acceleration; satellite imagery; telemetry workstation; spectroscopy; image processing; stellar spectra; optical radar; robotics; atmospheric composition; semiconductors computer networks; remote sensing; software engineering; solar flares; and glaciers.

Boroson, Harold R.↗

NASA NTRS1991

The High Energy Solar Physics mission (HESP): Scientific objectives and technical description

The High Energy Solar Physics mission offers the opportunity for major breakthroughs in the understanding of the fundamental energy release and particle acceleration processes at the core of the solar flare problem. The following subject areas are covered: the scientific objectives of HESP; what we can expect from the HESP observations; the high energy imaging spectrometer (HEISPEC); the HESP spacecraft; and budget and schedule.

Crannell, Carol↗

NASA NTRS1991

Simulations of pulsed electron beam injection during active experiments

Two-dimensional electromagnetic particle simulations are used to investigate the characteristics of the spacecraft charging, particle acceleration, and wave emissions during beam injection, turnoff and subsequent pulsing of the beam. It is shown that, during beam injection, the beam current is neutralized by a spatially separate return current region extending several tens of meters from the beam region, with the currents being closed across the field lines by the perpendicular acceleration of ambient plasma ions into the beam region. After beam turnoff, this current system reverses after a time lag of about an ion plasma period. The current reversal is accompanied by prolonged electron collection by the spacecraft near the beam region, preferential ion collection by sections of the spacecraft magnetically connected to the initial return current regions, and the creation of hot plasma extending well into the return current regions. Because of the time lag, the currents induced in the plasma during periodic beam injection can be strongly modified from the imposed beam current.

Winglee, R. M.↗

NASA NTRS1991

Computer simulation of astrophysical plasmas

The role of sophisticated numerical models and simulations in the field of plasma astrophysics is discussed. The need for an iteration between microphysics and macrophysics in order for astrophysical plasma physics to produce quantitative results that can be related to astronomical data is stressed. A discussion on computational requirements for simulations of astrophysical plasmas contrasts microscopic plasma simulations with macroscopic system models. An overview of particle-in-cell simulations (PICS) is given and two examples of PICS of astrophysical plasma are discussed including particle acceleration by collisionless shocks in relativistic plasmas and magnetic field reconnection in astrophysical plasmas.

Max, Claire E.↗

NASA NTRS1991

Plasma motions in planetary magnetospheres

Interplanetary space is pervaded by a supersonic 'solar wind' plasma; five planets, in addition to the earth, have magnetic fields of sufficient strength to form the cometlike cavities called 'magnetospheres'. Comparative studies of these structures have indicated the specific environmental factor that can result in dramatic differences in the behavior of any pair of magnetospheres. Although planetary magnetospheres are large enough to serve as laboratories for in situ study of cosmic plasma and magnetic field behavior effects on particle acceleration and EM emission, much work remains to be done toward relating magnetospheric physics results to the study of remote astrophysical plasmas.

Hill, T. W.↗

NASA NTRS1991

Transverse conductivity of a relativistic plasma in oblique electric and magnetic fields

Resistive tearing in a primary candidate for flares occurring in stressed magnetic fields. Its possible application to the strongly magnetized environments (Hz about 10 to the 12th G) near the surface of neutron stars, particularly as a mechanism for generating the plasma heating and particle acceleration leading to gamma-ray bursts, has motivated a quantum treatment of this process, which requires knowledge of the electrical conductivity sigma of a relativistic gas in a new domain (i.e., that of a low-density n/e/) plasma in oblique electric and magnetic fields. This paper discusses the mathematical formalism for calculating sigma and present numerical results for a wide range of parameter values. The results indicate that sigma depends very strongly on both the applied electric and magnetic fields.

Melia, Fulvio↗

NASA NTRS1991

Prompt arrival of solar energetic particles from far eastern events - The role of large-scale interplanetary magnetic field structure

Intensity-time profiles of solar energetic particle enhancements generally show an asymmetry with respect to the heliolongitude of the associated solar event. Particles arrive promptly from events to the west of an observer because of good magnetic connection, whereas particle enhancements from poorly connected eastern source regions usually show much slower onsets. However, some 15 percent of eastern events do show prompt onsets. Two prompt particle enhancements associated with eastern solar events are studied using data from the Goddard Space Flight Center instruments on the ISEE 3 and IMP 8 spacecraft. In both events the prompt particle onset was observed when the spacecraft were in a postshock plasma region, apparently within a magnetic bottle. It is suggested that the magnetic bottle extended back to the sun and served as a channel for fast particle propagation to the spacecraft. Particles accelerated at an expanding coronal shock initiated by the eastern event could be injected onto field lines in the foot of the bottle.

Richardson, I. G.↗

NASA NTRS1991

HST observations of 3C 66B - A double-stranded optical jet

The central region of the synchrotron jet in 3C 66B imaged with ultrahigh spatial resolution by the Faint Object Camera on the HST is discussed. A close correspondence between the general characteristics of the smoothed optical image and the radio map is observed, implying that the young and old relativistic particles occupy similar regions to within about 130 pc. Focus is placed on the double-stranded filamentary nature of the jet, and it is speculated that this could reflect edge-brightening effects due to enhanced radiation from a skinlike structure surrounding the jet. It is noted that the similarity of optical and radio morphologies points to the fact that localized particle acceleration occurs along the jet; however, the filamentary structure and a low filling factor of radiation agree with a model in which the electrons are accelerated within the nucleus and are transported along the jet in a channel having low magnetic field.

Macchetto, F.↗

NASA NTRS1990

Supernovae and supernova remnants at high energies

The physical phenomena that are observable with X- and gamma-ray observations of supernovae are discussed with respect to possible high-energy astrophysics experiments. Prompt photospheric emission and its echo are discussed, supernova radioactivity and neutron star effects are examined, and circumstellar and interstellar interaction are reviewed. The primary uncertainties are found to be the hardening of the spectrum by non-LTE effects and the amount of absorption of the radiation from the initial soft X-ray burst. The radioactivity in supernovae is theorized to lead to gamma-ray lines and continuum emission unless the event is low-mass type II. Gamma-ray observations are proposed to examine the efficiency of particle acceleration, and high-resolution spectroscopy can provide data regarding ionization, temperature, composition, and velocities of the X-ray-emitting gas.

Chevalier, Roger A.↗

NASA NTRS1990

The goals of gamma-ray spectroscopy in high energy astrophysics

The use of high resolution gamma-ray spectroscopy in astrophysics is discussed with specific attention given to the application of the Nuclear Astrophysics Explorer (NAE). The gamma-ray lines from nuclear transitions in radionucleic decay and positron annihilation permits the study of current sites, rates and models of nucleosynthesis, and galactic structure. Diffuse galactic emission is discussed, and the high-resolution observations of gamma-ray lines from discrete sites are also described. Interstellar mixing and elemental abundances can also be inferred from high-resolution gamma-ray spectroscopy of nucleosynthetic products. Compact objects can also be examined by means of gamma-ray emissions, allowing better understanding of neutron stars and the accreting black hole near the galactic center. Solar physics can also be investigated by examining such features as solar-flare particle acceleration and atmospheric abundances.

Lingenfelter, Richard E.↗

NASA NTRS1991

The formation of quasi-parallel shocks

In a collisionless plasma, the coupling between a piston and the plasma must take place through either laminar or turbulent electromagnetic fields. Of the three types of coupling (laminar, Larmor and turbulent), shock formation in the parallel regime is dominated by the latter and in the quasi-parallel regime by a combination of all three, depending on the piston. In the quasi-perpendicular regime, there is usually a good separation between piston and shock. This is not true in the quasi-parallel and parallel regime. Hybrid numerical simulations for hot plasma pistons indicate that when the electrons are hot, a shock forms, but does not cleanly decouple from the piston. For hot ion pistons, no shock forms in the parallel limit: in the quasi-parallel case, a shock forms, but there is severe contamination from hot piston ions. These results suggest that the properties of solar and astrophysical shocks, such as particle acceleration, cannot be readily separated from their driving mechanism.

Cargill, Peter J.↗

NASA NTRS1991

Magnetic field-aligned electric potentials in nonideal plasma flows

The electric field component parallel to the magnetic field arising from plasma flows which violate the frozen-in field condition of ideal magnetohydrodynamics is discussed. The quantity of interest is the potential U = integral E parallel ds where the integral is extended along field lines. It is shown that U can be directly related to magnetic field properties, expressed by Euler potentials, even when time-dependence is included. These results are applicable to earth's magnetosphere, to solar flares, to aligned-rotator models of compact objects, and to galactic rotation. On the basis of order-of-magnitude estimates, these results support the view that parallel electric fields associated with nonideal plasma flows might play an important role in cosmic particle acceleration.

Schindler, K.↗

NASA NTRS1991

Neutron starquake model for gamma-ray bursts

A neutron starquake model for gamma ray bursts is presented and critically analyzed. It is suggested that a slowly accreting neutron star may develop density inversions deep in its crust. These unstable layers, may be subject to elastic Rayleigh-Taylor instability which can liberate sufficient gravitational and perhaps also nuclear energy to account for individual bursts. Energy can be transported to the surface by shear waves and slowly transmitted into the magnetosphere as relativistic Alfven waves. Particle acceleration and gamma ray emission from the outer magnetosphere should ensue. Some observational implications are mentioned.

Blandford, R. D.↗

NASA NTRS1992

Flare gamma ray continuum emission from neutral pion decay

We investigate, in detail, the production of solar flare gamma ray emission above 100 MeV via the interaction of high energy protons with the ambient solar atmosphere. We restrict our considerations to the broadband gamma ray spectrum resulting from the decay of neutral pions produced in p-H reactions. Thick-target calculations are performed to determine the photon fluences. However, proton transport is not considered. Inferences about the form of the proton spectrum at 10-100 MeV have already been drawn from de-excitation gamma ray lines. Our aim is to constrain the proton spectrum at higher energies. Thus, the injected proton spectrum is assumed to have the form of a Bessel Function, characteristics of stochastic energy at higher energies. The detailed shape of the gamma ray spectra around 100 MeV is found to have a strong dependence on the spectral index of the power law and on the turnover energy (from Bessel function to power law). As would be expected, the harder the photon spectrum the wider the 100 MeV feature. The photon spectra are to be compared with observations and used to place limits upon the number of particles accelerated and to constrain acceleration models.

Alexander, David↗