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At least 1,261 records · Page 70
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NASA NTRS1984

3 keV to 2 MeV observations of four gamma-ray bursts

Simultaneous X and gamma ray spectra were obtained for four gamma ray burst events using satellite instrumentation. The P78-1 satellite proportional counters recorded X-ray data in the 3-10 keV range, while Pioneer Venus Orbiter and ISEE 3 sensors had a 3 keV lower limit for events. The positively correlated data covered the events GB 790307, 790325, 790504, and 790731. The time histories of the X and gamma ray energies did not correlate well. The post-gamma ray phase of GB 790307 displayed features of simple cooling, and in conjunction with soft X-ray data suggested an origin in an optically thin fireball. However, the data were equally well-fitted by a model of an emitting hot spot on a neutron star. The data negated any concept that gamma ray bursts evolve similarly to classical X-ray bursts.

Laros, J. G.↗
NASA NTRS1984

Ionic charge states of N, Ne, Mg, Si and S in solar energetic particle events

The mean ionic charges and source-region temperatures of flare-accelerated N, Ne, Mg, Si and S in three large solar-energetic-particle events during 1978-1979 are determined from ISEE-3 observations, extending the findings of Hovestadt et al. (1981) and Gloeckler et al. (1981) for C, He, O, and Fe. The results are presented in tables and graphs, and the charge states are shown to correspond to different source temperatures even in the same flare, assuming equilibration in the hot plasma. The electron temperatures range from 2 x 10 to the 6th K for C, N, O, Si, and S, 4 x 10 to the 6th K for Ne and Fe, and 7 x 10 to the 6th K for Mg. The possibility that these temperature inconsistencies reflect different stages in the approach to equilibrium is considered.

Luhn, A.↗
NASA NTRS1984

The physical mechanisms of subcritical collisionless shock-wave formation

The key process in shock wave formation is related to energy dissipation, and the nature of the operative dissipation mechanism determines the basic character of the resulting shock. In the case of collisionless plasmas, the primary problem consists in the identification of the processes which can provide the necessary dissipation in relatively short spatial scale lengths. The present investigation is concerned with the various collisionless dissipation mechanisms which can operate in weak shocks, taking into account the effects of different mechanisms on shock structure. Particular attention is given to a restricted class of quasi-perpendicular low beta low Mach number shocks. Such shocks are traditionally called 'laminar shocks'. Resistive shocks are considered along with subcritical shocks observed with the aid of the ISEE spacecraft.

Mellott, M. M.↗
NASA NTRS1983

The interplanetary shock event of November 11/12 1978 - A comprehensive test of acceleration theory

A comprehensive study of the November 11, 12, 1978 shock event based on energetic particle, solar wind, magnetic field and wave data from the ISEE-3, -1 and -2 spacecraft has been undertaken both from the energetic and the collisionless shock point of view. The energy density of 10-50 keV protons accelerated by the shock is found to be equivalent to the upstream magnetic field energy density. The observations are in quantitative agreement with Lee's (1983) self consistent theory for the excitation of hydromagnetic waves and the acceleration of ions upstream of interplanetary shocks.

Wenzel, K.-P.↗
NASA NTRS1983

The September 1979 solar cosmic ray event

Observations of a long-lived solar particle event in September 1979, are presented. The energy flux observations were carried out simultaneously by the Voyager 2, ISEE-3, and IMP-8 satellites at widely separated radial positions. It is shown that the flux spectra of the particle population which arrived early at Voyager 2 extended to several MeV for each nucleon, although at energies above 1.5 MeV/nuc, the peak flux occurred one day later. The solar wind speed at Voyager 2 increased from about 600 km/s to 1000 km/s upon the arrival of the particles, causing rapid changes in the Voyager 2 connection longitude. It is suggested that the steepening observed in the maximum flux energy spectra above about 10 MeV/nuc at Voyager 2 may have been due to the injection of particles one day earlier.

Hamilton, D. C.↗
NASA NTRS1983

Ionization states of helium in He-3-rich solar energetic particle events

Results of a systematic study of the ionic charge state of helium in the energy range 0.6-1.0 MeV/nucleon for He-3-rich solar energetic particle events during the time period August 1978 to October 1979 are reported. The data have been obtained with the Max-Planck-Institut/University of Maryland experiment on ISEE-3. Whereas for solar energetic particle events with no enrichment of He-3 relative to He-4 surprisingly large abundances of singly ionized helium have been reported recently, He-3-rich solar energetic particle events do not show significant abundances of He-3(+). This result is consistent with current theories explaining large compositional anomalies by mass per charge dependent selective heating of the minor ion species.

Klecker, B.↗
NASA NTRS1983

Direct determination of the ionic charge distribution of heavy ions in Fe-rich solar energetic particle events

The first direct determination of the iron charge distribution in the energy range 0.3-1.0 MeV/nucleon during Fe-rich and He-3-rich solar energetic particle events is reported. The deterimination was made on the basis of ISEE-3 data for the event from August 1978 to October 1979. The enrichment of He-3 iron relative to oxygen was found to be directly correlated with the enrichment of He-3 to He-4. Average ion charge distributions were computed for: (1) He-3-rich periods which were also Fe-rich and had a He-3/He-4 ratio of 0.1 and (2) periods with a He-3/He-4 ratio of less than 0.1. It is found that the mean iron charge state for He-3-rich periods was in the range 19.5 (+ or - 1.5) and only 14 (+ or - 1) for the time periods with He-3/He-4 less than ratio of 0.1. The reduced data are found to be in good agreement with the theoretical predictions of Fisk (1978), suggesting a temperature in the source region above 5 million degrees K for Fe-rich and He-3-rich solar energetic particle events.

Klecker, B.↗
NASA NTRS1983

The delayed energetic particle event of June 6-10, 1979

Energetic particle observations carried out with the ISEE-3 Medium-Energy Cosmic Ray experiment during the flare event of June 6-10, 1979 are reported. An expanded time history of the He nuclei particle spectra is given, and particle trajectory angles are identified with respect to the earth-sun line. The backward flow of the particle stream following the shock was analyzed, and it is found that the shock continued to accelerate particles beyond 1 AU from the sun. Polar plots of the number of protons counted in each sector of observation are given with their corresponding magnetic field directions.

Von Rosenvinge, T. T.↗
NASA NTRS1985

Coupling between the solar wind and the magnetosphere - CDAW 6

It is pointed out that an extensive study of the causes and manifestations of geomagnetic activity has been carried out as part of the sixth Coordinated Data Analysis Workshop, CDAW 6. The present investigation has the objective to determine the coupling between the solar wind and the magnetosphere for the two selected analysis intervals, taking into account, as a basis for the study, the interplanetary field and plasma observations from ISEE 3 and IMP 8 and the geomagnetic activity indicators developed by CDAW 6 participants. The method of analysis employed is discussed, giving attention to geomagnetic indices, upstream parameters, and a cross-correlation analysis. In a description of the obtained results, the March 22, 1979 event is considered along with the March 31 to April 1, 1979 event, and an intercomparison of the events. The relationship between interplanetary indices and the resulting geomagnetic activity for the two CDAW 6 intervals is illustrated.

Tsurutani, B. T.↗
NASA NTRS1985

Substorm effects on the plasma sheet ion composition on March 22, 1979 (CDAW 6)

One of the potentially most useful aspects of mass spectroscopy in magnetospheric research is related to the ability to distinguish between ions of solar wind and terrestrial origins. Knowing the source of the plasmas in various regions and under various geomagnetic conditions is crucial in improving the understanding of particle flows in the magnetosphere. Sharp et al. (1982) found that the plasma sheet ions in the 0.1- to 16-keV/e range, were predominantly of solar wind origin during low geomagnetic activity, while there was a large terrestrial component during active times. This paper presents a set of data from March 22, 1979. The reported investigation represents the first detailed case study of the relation between geomagnetic substorm activity and the ion composition in the plasma sheet. A decrease in solar wind ion flow at ISEE 1 and the subsequent increase in the flow of ionospheric ions is interpreted as evidence of a fundamental change in the particle flow pattern following the start of substorm activity.

Lennartsson, W.↗
NASA NTRS1985

Short-wavelength electrostatic waves in the earth's magnetosheath

Recent observations with the ISEE-1 spacecraft have found electric field emissions in the dayside magnetosheath whose frequency spectrum is modulated at twice the spacecraft spin period. The upper frequency cut-off in the frequency-time spectrum of the emissions has a characteristic parabola shape or festoon shape. The low frequency cutoff ranges from 100 Hz to 400 Hz, while the high frequency limit ranges from about 1 kHz to 4 kHz. The bandwidth is found to minimize for antenna orientations parallel to the wave vectors. The wave vector does not appear to be related to either the local magnetic field direction of the plasma flow velocity. The spacecraft observed frequency spectrum results from the spacecraft antenna response to the Doppler shifted wave vector spectrum which exists in the plasma. Imposed constraints on the plasma restframe wave vectors and frequencies indicate that the emissions occur within the frequency range from about 150 Hz to 1 kHz, with wavelengths between about 30 meters and 600 meters. These constraints strongly suggest that the festoon-shaped emissions are ion-acoustic waves. The small group velocity and k direction of the ion-acoustic mode are consistent with wave generation upstream at the bow shock and convection downstream to locations within the outer dayside magnetosheath.

Gallagher, D. L.↗
NASA NTRS1984

The international Halley Watch

The schedule of ground-based and extraterrestrial observations planned for comet Halley during the International Halley Watch (IHW) program is briefly described. A schematic diagram is presented in order to illustrate the lines of communication between the administrators, discipline specialists, and amateur observers participating in IHW. The specific observational activities schedule for the IHW in early late 1985 and early 1986 include: infrared spectroscopic and radiometric observations; photometry and polarimetry, and near nucleus studies. The satellite observation platforms of the IHW will include, the Giotto, VEGA, ISEE-3, and Plant A satellites.

West, R. M.↗
NASA NTRS1985

Characteristics of the white-light source in the 1981 April 24 solar flare

Observations of the white-light solar flare event of April 24, 1981 are presented. The observations were carried out in the optical, hard X-ray, and radio wavelengths from land-based observatories and from the International Sun-Earth Explorer (ISEE-3) satellite. Time-intensity profiles were derived for three lines of continuum emissions. The derived profiles are interpreted in terms of the energetics of the flare, and the role of energetic electrons in the production of optical continuum emission is examined in detail.

Kane, S. R.↗
NASA NTRS1985

The polar ionosphere as a source of the storm time ring current

The transport of ions from the polar ionosphere to the inner magnetosphere during storm time conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the rate of energization of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double-spiral injection boundary. Inward of the injection boundary the ions were convected adiabatically. By using as input an O(+) flux of 2.8 x 10 to the 8th per sq cm per s (w greater than 10 eV) and an H(+) flux of 5.5 x 10 to the 8th per sq cm per s (w greater than .63 eV) the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range in L (4-8), with measurements made with the ISEE 1 satellite during a storm. This O(+) flux and a large part of the H(+) flux appear to be consistent with the DE-1 and DE-2 satellite measurements of the polar ionospheric outflow during disturbed times.

Cladis, J. B.↗
NASA NTRS1985

A comparison of solar helium-3-rich events with type II bursts and coronal mass ejections

The acceleration process for energetic particles in He-3-rich events and for particles in normal-abundance events are compared. A list of 66 He-3-rich events observed with the Goddard Space Flight Center particle detector on ISEE 3 is presented, and it is shown that these events are not statistically associated with either of the two common signatures of normal-abundance events, metric type II and coronal mass ejections. This result indicates that enhanced abundance events may be produced only in the impulsive phases of flares, while normal abundance events are produced in subsequent flare shock waves.

Kahler, S.↗
NASA NTRS1985

Configuration of the high-latitude thermosphere neutral circulation for IMF B(y) negative and positive

Asymmetries in the Northern Hemisphere neutral circulation that are dependent on the sign of the east-west 'B(y)' component of the IMF are presently illustrated by measurements of the neutral wind in the polar F-region which were conducted by the DE-2 spacecraft. The data thus obtained are categorized according to the sign of the hourly averaged IMF B(y) component measured by ISEE-3 for the hour preceding the DE-2 measurements. It is noted that there is (1) an asymmetry in the polar cap neutral flow velocity, with the region of most rapid antisunward flow shifting from the dawn side to the dusk side of the polar cap as B(y) changes from positive to negative; (2) a shift occurs in the magnetic local time of the region of entry of neutral gas into the polar cap, from a location on the dawn side of the moon-midnight meridian for B(y) positive to one more biased, for B(y) negative; and (3) there is an enhancement of velocities associated with the dawn anticlockwise neutral vortex for B(y) negative relative to those observed for B(y) positive.

Mccormac, F. G.↗
NASA NTRS1985

New results on the Pioneer Venus Orbiter February 10-11, 1982 events - A solar wind disturbance not a comet

The characteristics of a series of disturbances observed on February 10-11, 1982 by the plasma analyzer and the magnetometer on the Pioneer Venus Orbiter, obtained in the solar wind upstream of Venus are studied. It is concluded that the events were associated with the propagation of a solar wind disturbance of coronal origin and not with an encounter with a comet or other local outgassing object (Russel, et al., 1983). The plasma analyzer spectra clearly show the presence of increases in He(2) and they argue strongly against Russell, et al.'s interpretatation. The peak in magnetic field magnitude on February 11 is identified as the magnetic signature of a thin, trailing 'filament' at the end of a series of solar-initiated events. Corresponding increases in He(2) and magnetic field fluctuations were observed near earth by ISEE-3 about a day later, and this strongly supports the concept of a solar origin.

Intriligator, D. S.↗
NASA NTRS1985

Energetic particle characteristics of magnetotail flux ropes

During the recent ISEE-3 Geotail Mission three events have been identified from the magnetometer data which are consistent with a spacecraft crossing of a magnetotail flux rope. Energetic electron and proton observations obtained by the Max-Planck-Institut/University of Maryland sensor system during two of the possible flux rope events are presented. During one event remote sensing of the flux rope with energetic protons reveals that the flux rope is crossed by the spacecraft from south to north. This allows determination of the bandedness of the magnetic field twist and of the flux rope velocity relative to the spacecraft. A minimal flux rope radius of 3 earth radii is derived. Energetic proton intensity is highest just inside of the flux rope and decreases towards the core. Energetic electrons are streaming tailward near the outer boundary, indicating openness of the field lines, and are isotropic through the inner part of the flux rope.

Scholer, M.↗