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At least 1,009 records · Page 56
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NASA NTRS1979

Gamma-ray burst observations by Pioneer Venus Orbiter

The Pioneer Venus Orbiter gamma burst detector is an astrophysics experiment for monitoring cosmic gamma-ray bursts. It is included in this planetary mission to provide a long baseline for accurately locating the sources of these bursts in order to identify them with specific astronomical objects. Responses to 14 gamma-ray burst events were examined; these events were verified from data acquired by other systems. Preliminary locations are proposed for three events, based on data from the Pioneer Venus Orbiter, ISEE C, and Vela spacecraft. These locations will be improved, and additional locations will be determined by including in the analyses data from Helios B and the Russian Venera 11, Venera 12, and Prognoz 7 spacecraft.

Evans, W. D.↗
NASA NTRS1978

Interconnecting conductively coated coverslides

The International Sun Earth Explorer-1 has the requirement that the entire outer surface of the spacecraft be conductive. A transparent coating of indium oxide was deposited for that reason on the satellite's solar cell coverglasses in order to give them a conductive surface, and the surfaces were interconnected to ground. This paper examines the interconnector attachment problem. On the ISEE-1, wires were bonded to the coverglasses by using a conductive epoxy; the resistance of these bonds increased dramatically with time. A program was initiated to find the functional cause of the resistance increase and to flight-qualify an alternative method of bonding. It was found the tests initiated were insufficient to find the cause of resistance increase and that an alternative solution of using indium solder is acceptable for bonding wires directly to indium oxide.

Gaddy, E. M.↗
NASA NTRS1979

A comparison of intense electrostatic waves near f-UHR with linear instability theory

Intense electrostatic waves near the upper hybrid resonance frequency (f-UHR) have recently been detected near but beyond the plasmapause between + or -50 deg magnetic latitude at all local times. The paper shows that the electrostatic waves observed with the ISEE 1 plasma wave receiver near f-UHR are in qualitative agreement with linear theory of multicyclotron harmonic emissions. The peak amplitudes and bandwidths observed are similar to those calculated for maximum spatial growth rates. Measurements on Hawkeye of similar waves suggest that the electric field polarization is also consistent with theory. For a wide range of plasma parameters, nonconvective instability or large spatial growth rates occur within the cyclotron band encompassing the cold upper hybrid frequency.

Kurth, W. S.↗
NASA NTRS1978

The cosmic ray nuclides

The relative abundances of individual nuclides in cosmic rays are discussed. Data on the H-He nuclide quartet are reviewed, along with experimental results for stable nuclides with Z of at least 3. Detailed attention is given to the ratios C-12/C-13, N-15/N, and O-17+18/O, as well as to the light-heavy nuclei, the iron group, and radionuclides. The resolution of the low- and medium-energy detectors aboard the ISEE satellite is illustrated.

Waddington, C. J.↗
NASA NTRS1979

Direct observation of a tangential electric field component at the magnetopause

Results are presented for direct, in situ measurements of the quasi-static electric field at and near the magnetopause, in the magnetosheath, bow shock, and solar wind, obtained by the ISEE-1 satellite. Both the large-scale average electric field and the fine-scale field observed during a magnetopause crossing show the existence of significant tangential electric field components on both sides of the magnetopause. The data in the satellite frame also show significant normal electric field components that point toward the magnetopause on both sides. The observed local level of power dissipation would correspond to a total power of 1 TW, if it existed over the entire front of the magnetopause.

Mozer, F. S.↗
NASA NTRS1979

H/+/ and He/2+/ in the dawnside magnetosheath

Mass and energy analyses of energetic ions in the dawnside magnetosheath have been made by the energetic ion composition experiment on the ISEE-1 spacecraft over the energy range 10 eV/e to 17 keV/e. The significant observations are: the bulk flows of the H(+) and He(2+) components determined from first moments of the distributions averaged over several minutes are equal within the uncertainties of the measurement. The H(+) and He(2+) distributions are similar in that they both show temperature anisotropies with perpendicular temperature not less than parallel temperature; however, the distributions are not well characterized by temperatures derived from second moments. In at least one case high energy tails of both distributions can be characterized by an additional higher temperature component. The major difference between the H(+) and He(2+) distributions is the depletion of the low velocity (in the center of mass frame) part of the He(2+) distributions, relative to the H(+) distributions.

Peterson, W. K.↗
NASA NTRS1979

Pitch angle distributions of energetic protons near the earth's bow shock

Measurements of energetic protons between about 28 and about 145 keV on ISEE-1 upstream and downstream of the earth's bow shock during times of a radial interplanetary magnetic field are presented. The protons exhibited a slight antisunward flow in the spacecraft system in front of the bow shock and a strong flow along the magnetic field in the spacecraft system in the magnetosheath. Compton-Getting transformations of these anisotropies into the plasma frame of reference have been performed. It is argued that the observations can be explained best in terms of particle acceleration by multiple reflection between the bow shock and upstream scattering centers.

Scholer, M.↗
NASA NTRS1979

Magnetopause Kelvin-Helmholtz instability

The Kelvin-Helmholtz instability as it applies to the dayside magnetopause is reviewed. Simple theory suggests the boundary should generally be unstable to waves moving at a large angle to the Earth's field. Nonlinear effects, how amplitudes might be limited, and what dynamic role the instability could have in boundary regions in stimulating mass and momentum transfer are discussed. Examination of data from a particular ISEE spacecraft pass shows relatively small amplitude (750 km) waves present on the boundary. Corresponding wavelength estimates show wave momentum is not significant at the time of the pass.

Southwood, D. J.↗
NASA NTRS1980

The Goddard program of gamma ray transient astronomy

Gamma ray burst studies are reviewed. The past results, present status and future expectations are outlined regarding endeavors using experiments on balloons, IMP-6 and -7, OGO-3, ISEE-1 and -3, Helios-2, Solar Maximum Mission, the Einstein Observatory, Solar Polar and the Gamma Ray Observatory, and with the interplanetary gamma ray burst networks, to which some of these spacecraft sensors contribute. Additional emphasis is given to the recent discovery of a new type of gamma ray transient, detected on 1979 March 5.

Cline, T. L.↗
NASA NTRS1979

Plasma acceleration at the earth's magnetopause - Evidence for reconnection

Observations of high-speed plasma at the magnetopause in agreement with theoretical predictions of magnetic field reconnection are reported. Plasma ion and electron distributions measured by the quadrispherical analyzers on board the ISEE 1 and 2 spacecraft were obtained during the outbound traversal of the subsolar magnetopause. Plasma flow speeds of up to 450 km/sec were observed in the magnetopause layer, in contrast to speeds of 50 to 100 km/sec in the adjacent magnetosheath. The observations agree with the predictions of the reconnection model of the dayside magnetopause, in which the magnetopause is described as a rotational discontinuity, or a large-amplitude Alfven wave. It is noted that the lack of observations of plasma acceleration in most other cases of favorable magnetic field orientation could be a product of the rarity of magnetic recombination, or its small scale and nonstationarity.

Paschmann, G.↗
NASA NTRS1979

Observation of an impulsive solar X-ray burst from a coronal source

Observations of the spatial, spectral, and temporal structure of an impulsive hard X-ray source in a behind-the-limb solar flare have been made with high-time-resolution hard X-ray detectors aboard two spacecraft, the International Sun Earth Explorer 3 (ISEE 3) and the Pioneer Venus Orbiter (PVO), which were separated in heliographic longitude by about 12.5 deg. The principal findings are that (1) the coronal part of the X-ray source is about 600 times less intense than the lower-altitude part of the source; and (2) the coronal X-ray observations are consistent with a power-law electron spectrum which extends down to about 5 keV.

Kane, S. R.↗
NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗
NASA NTRS1980

High resolution measurements of galactic cosmic-ray neon, magnesium, and silicon isotopes

High-resolution measurements of the abundances of individual isotopes of neon, magnesium and silicon in galactic cosmic rays are reported. The Caltech Heavy Isotope Spectrometer Telescope on board the ISEE 3 spacecraft was used to obtain measurements in the range 30 to 180 MeV/n at an rms mass resolution of 0.20 amu. Results indicate excesses of Ne-22 as well as Mg-25 and Mg-26 in galactic cosmic rays with respect to their solar system abundances. Calculations of the effects of interstellar propagation and solar modulation on cosmic-ray isotope abundances also imply an Mg-25 + Mg-26 cosmic ray source fraction significantly greater than the solar system fraction, and it is suggested that the cosmic ray source material and solar system material were synthesized under different conditions.

Mewaldt, R. A.↗
NASA NTRS1980

Solar wind ions accelerated to 40 keV by shock wave disturbances

Observations in the solar wind with the LASL/MPI fast plasma experiment on ISEE 1 and 2 reveal the common presence of ions with energies extending from 100 eV up to at least 40 keV in a broad region, typically 10 million kilometers wide, following interplanetary shocks. Peak differential fluxes up to 5000/sq cm s sr keV at 28 keV are observed either at the shock or within the first 1.5 hours following shock passage. In the solar wind frame the distribution function of these ions is roughly isotropic, peaks near zero velocity, and above 5 keV can adequately be characterized as power law in energy with a spectral index of 2.7. The effective 'temperature' of these ions generally exceeds 100 million K. These suprathermal interplanetary ions are almost certainly solar wind ions which have been accelerated by some mechanism associated with the shock wave disturbance. Present evidence leads the authors to favor stochastic particle acceleration involving electrostatic and/or electromagnetic turbulence in the postshock flow.

Gosling, J. T.↗
NASA NTRS1980

High-resolution spectroscopy of two gamma-ray bursts in 1978 November

The first results from the ISEE 3 radiatively cooled germanium gamma-ray burst spectrometer are presented. Spectra and time histories from two events on 1978 November 4 and 19 are given. A significant difference in the continuum spectra for the two events was observed. Evidence is presented for two spectral features in the November 19 event, a broad one at about 420 keV and a narrower one at about 740 keV with a suggestion of an accompanying high-energy tail.

Teegarden, B. J.↗
NASA NTRS1980

Impulsive 2-10 keV solar electron events not associated with flares

Data from the ISEE 3 satellite reveal a class of impulsive solar electron events with no measurable increase in flux above 10-20 keV. The flux histories and angular distributions indicate that the electrons propagate through interplanetary space with little or no scattering. The smooth extension of the power-law energy spectra down to the limit of the observations at 2 keV indicates that the electrons are accelerated at altitudes greater than 0.5 solar radii in the solar corona. Although these events occur more frequently than any other type of impulsive solar particle event observed, no correlation is found with flares or flare-related activity. However, there is a close correlation with low-frequency type III radio bursts.

Potter, D. W.↗
NASA NTRS1980

On the convective properties of magnetospheric Bernstein waves

Recent plasma wave observations made by the ISEE and GEOS satellites of the electrostatic cyclotron harmonic waves have been consistent with and organized very well within the theoretical framework of Bernstein waves excited in magnetospheric plasma. Attention is given to an examination of a number of effects that result simply from the convective properties of Bernstein waves in a magnetospheric plasma environment. The roles of wave trapping in plasma density depressions and partial trappings near the magnetic equator are discussed. Certain future wave observations are suggested that can improve the understanding of this magnetospheric wave phenomenon.

Barbosa, D. D.↗
NASA NTRS1980

The volume emissivity of type III radio bursts

The volume emissivity has been calculated for thirty-six type III solar radio bursts obtained from approximately 6.5 years of Imp 8 and ISEE 1 satellite data. Although the emissivities for these events vary over a large range, all the emissivities decrease rapidly with increasing heliocentric radial distance. The best fit power law for the emissivity, using the average power law index for all events analyzed, is J = J(0)R(-6.0), with J0 = 1.5 x 10 to the -24th W/cu m sr. This best fit emissivity is used to estimate the expected radial variation of the plasma oscillations responsible for the type III radio emissions.

Tokar, R. L.↗