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NASA NTRS1986

Nineteenth International Cosmic Ray Conference. Conference Papers: Invited Rapporteur, Highlight, Miscellaneous, Volume 9

Invited talks, rapporteur talks, and highlight talks are included. Topics of the invited and highlight talks include astrophysical jets, gamma-ray line astronomy, cosmic rays and gamma rays in astrophysics, the early universe, elementary particle physics, solar flares and acceleration of energetic particles, cosmogenic nuclei, extragalactic astronomy, composition of solar flare particles, very high energy gamma ray sources, gamma-ray bursts, shock acceleration in the solar wind, cosmic rays in deep underground detectors, spectrum of cosmic rays at 10 to the 19th power eV, and nucleus-nucleus interactions.

Jones, F. C.↗
NASA NTRS1986

Lead, platinum and other heavy elements in the primary cosmic radiation: HEAO-3 results

An observation of the abundances of cosmic-ray lead and platinum-group nuclei using data from the HEAO-3 Heavy Nuclei Experiment (HNE) which consisted of ion chambers mounted on both sides of a plastic Cherenkov counter (Binns et al., 1981) is reported. Further analysis with more stringent selections, inclusion of additional data, and a calibration at the LBL Bevalac, have allowed the determination of the abundance ratio of lead and the platinum group of elements for particles that had a cutoff rigidity R(c) 5 GV. The observed ratio for Pb/Pt is distinctly lower than that predicted by any of the standard models for cosmic ray sources. It is possible that the difference is not an indication that the cosmic ray source composition is greatly different from that of the solar system, but rather that there is less Pb in the solar system and in the r-process than is assumed in the standard models.

Waddington, C. J.↗
NASA NTRS1985

Gradients and anisotropies of high energy cosmic rays in the outer heliosphere

Two cosmic rays which pass through the same point going in opposite directions will, in the absence of scattering and inhomogeneities in the magnetic field, trace helices about adjacent flux tubes, whose centerlines are separated by one gyrodiameter. A directional anisotropy at the point suggests a difference in the number of cosmic rays loading the two flux tubes; that is, a density gradient over the baseline of a gyrodiameter. Previous studies at lower energies have shown that the cosmic ray density gradients vary in time and space. It is suggested that the radial gradient associated with solar cycle modulation is supported largely by narrow barriers which encircle the sun and propagate outward with the solar wind. If so, the anisotropy is a desirable way to detect spatial gradients, because it can be associated with the local solar wind and magnetic field conditions. Anisotropic measurements made by Cerenkov detectors on Pioneers 10 and 11 were studied. It was found that local anisotropy varies greatly, but that the long term average is consistent with the global radial gradient measured between two spacecraft over a baseline of many AU.

Fillius, W.↗
NASA NTRS1985

Cosmic-ray acceleration at stellar wind terminal shocks

Steady-state spherically symmetric analytic solutions of the cosmic-ray transport equations, applicable to the problem of acceleration of cosmic rays at the terminal shock to a stellar wind, are studied. The spectra, graidents, and flow patterns of particles modulated and accelerated by the stellar wind and shock are investigated by means of monoenergetic-source solutions at finite radius, as well as solutions with monoenergetic and power-law galactic spectra. On the basis of calculations given, early-type stars could supply a significant fraction of the 3 x 10 to the 40th ergs/sec required by galactic cosmic rays.

Webb, G. M.↗
NASA NTRS1985

The heaviest cosmic-ray nuclei

The implications of abundance measurements of cosmic-ray nuclei heavier than Fe are examined in light of standard propagation models and nucleosynthetic theory. Suggestions that the cosmic-ray source abundances differ significantly from solar system abundances are not well supported by the data without assuming ad hoc models of preferential acceleration. The solar system abundances of Pb and Bi are split into r-, standard s-, and cyclic s-process components to assess the contributions of these nucleosynthetic processes to the cosmic-ray source. The apparent deficiency of Pb seen in the HEAO 3 HNE data might indicate an absence of Pb from the recycling s-process.

Margolis, S. H.↗
NASA NTRS1986

The cosmic-ray source composition

The cosmic-ray source composition is shown to be related to the observed cosmic-ray abundances by a set of linear equations which are valid for either ad hoc path length distributions or quantitative solutions of galactic propagation models. In the limit of no ionization energy loss, this method is exact for all path length distributions and can replace more detailed numerical integrations; it provides a simple way to calculate directly the source composition implied by a particular set of cross sections, observed abundances, and propagation model. This method is used to determine the source abundances of the galactic cosmic rays in a model-independent manner. Compared to a simple exponential, the path length distribution required by observations is deficient in the contributions from short (not greater than 0.5 g/sq cm) paths at energies of a few GeV per nucleon.

Margolis, S. H.↗
NASA NTRS1986

Will cosmic strings be discovered using the Space Telescope?

Cosmic strings are topologically stable defects in the vacuum of space which may be produced by a phase transition in the early universe. Here, it is suggested that observations of very distant galaxies are a more useful means of discovering strings than quasar observations. It is argued that if there is only one string out to redshift z - about 1 the probability that it crosses a random image obtained using the Wide Field Camera (WFC) of the Space Telescope is about 0.0001. In order to discover a cosmic string the Space Telescope WFC will be required to operate almost continuously in primary and serendipity modes, and a cosmic string, if it exists, may be discovered within the first few years of operation.

Pacynski, B.↗
NASA NTRS1986

Characteristic recovery times of Forbush-type decreases in the cosmic radiation. I - Observations at earth at different energies

Data on 30 asymmetric Forbush decreases recorded by the IMP spacecraft at 1 AU and the Mt. Washington neutron monitor over the period 1972-84 are examined to characterize the recovery characteristics of cosmic rays after the events. The spacecraft data are concentrated at energies of 1.7 GV, while the terrestrial instruments recorded events at 5 GV. Attention is paid to the relative amplitudes of the recorded transient decreases, the characteristic recovery times, and the energy dependence of the amplitudes and recovery time. The recovery times were found to be equal at both energy levels, supporting a concept of energy independence for the recoveries. Also, no correlations were found between the recovery times and the occurrences of a solar magnetic field reversal or with phase in the solar modulation cycle. A time-dependent, two-dimensional model is defined, which expresses the cosmic ray particle distributions as a function of the decay of the disturbance, with a small dependence on the transport parameters of the cosmic rays.

Lockwood, J. A.↗
NASA NTRS1986

Differential measurement and model calculations of cosmic ray latitudinal gradient with respect to the heliospheric current sheet

Simultaneous magnetic field and charged particle measurements from the Voyager spacecraft with heliographic latitude separations of more than 10 deg are used to investigate the distribution of about 1-GeV galactic cosmic ray protons with respect to the heliospheric current sheet in the outer solar system. By comparing the ratio of cosmic ray flux at Voyager 1 to that at Voyager 2 during periods of relatively quiet interplanetary conditions when the spacecraft are either both north or both south of the heliospheric current sheet, an average latitude component of the gradient of the cosmic ray flux on opposite sides of the current sheet is derived under restricted interplanetary conditions of -0.22 + or - 0.03 pct/deg, equivalent to a decrease of about 1 percent/AU away from the current sheet at about 12 AU. The results for these limited periods are in qualitative agreement with propagation models incorporating particle drifts.

Christon, S. P.↗
NASA NTRS1986

Measurements of hydrogen and helium isotopes in Galactic cosmic rays from 1978 through 1984

The propagation of light cosmic rays is examined using measurements of the relative abundances of the isotopes H-1, H-2 and He-3 and He-4 made with the ISEE 3 instrumentation. It is believed that cosmic ray particles experience spallation in traveling through the interstellar medium, thereby producing the isotopes examined in the present study. The isotopic ratios are therefore expected to yield data on outward migrating particles, which lose energy while moving toward extragalactic space, i.e., the 'leaky box approximation'. The energy ranges covered are 26-138 MeV/nucleon for H-1 and He-4, 24-89 MeV/nucleon for H-2 and 43-146 MeV/nucleon for He-3. Solar activity ranged from minimum to maximum over the observational period. Details of the experimental strategies, instrumentation features and calibration techniques employed with the particle detectors are provided. Histograms were geneated of the energies attributable to each particle track and mass ratios of the various isotopes were calculated over the measured energy ranges. Account was taken of errors introduced by solar modulation, and an escape path length of 5.6-7.8 g/sq cm was estimated for particle propagation through the Galaxy. The projected path length agrees with previous estimates based on data from heavier cosmic ray nuclei.

Kroeger, R.↗
NASA NTRS1986

Enhancement of high-energy cosmic-ray spectrum by type-II supernovae

The cosmic-ray spectrum has an intensity enhancement in the energy range 10 to the 14th to 10 to the 16th eV per nucleus. Recent observations of heavy cosmic rays in this energy range indicate that the Ca/Fe ratio may be as large as 10 times the solar value. It is suggested that pulsars in type-II supernova remnants are the origin of this component of the cosmic-ray spectrum.

Takahashi, Y.↗
NASA NTRS1985

Detectors for high energy cosmic rays on Spacelab

Two instruments designed to determine the spectra of the individual cosmic-ray components at very high energies are described. One of these (CRNE) uses a combination of gas Cerenkov counters and transition radiation detectors for the cosmic-ray nuclei lithium to nickel; the other (TRIC) is optimized for the light cosmic rays (electrons, protons, helium) and uses a transition-radiation/ionization-calorimeter combination. The CRNE instrument, constructed at the University of Chicago, was delivered to NASA for a first Shuttle flight on Spacelab-2 in summer 1985. Some of the technical and programmatic requirements encountered during the hardware construction and integration are discussed, and the expected scientific return and the prospects of using such instrumentation on the Space Station are considered.

Lheureux, J.↗
NASA NTRS1987

IONS (ANURADHA): Ionization states of low energy cosmic rays

IONS (ANURADHA), the experimental payload designed specifically to determine the ionization states, flux, composition, energy spectra and arrival directions of low energy (10 to 100 MeV/amu) anomalous cosmic ray ions of helium to iron in near-Earth space, had a highly successful flight and operation Spacelab-3 mission. The experiment combines the accuracy of a highly sensitive CR-39 nuclear track detector with active components included in the payload to achieve the experimental objectives. Post-flight analysis of detector calibration pieces placed within the payload indicated no measurable changes in detector response due to its exposure in spacelab environment. Nuclear tracks produced by alpha-particles, oxygen group and Fe ions in low energy anomalous cosmic rays were identified. It is calculated that the main detector has recorded high quality events of about 10,000 alpha-particles and similar number of oxygen group and heavier ions of low energy cosmic rays.

Biswas, S.↗
NASA NTRS1987

Cosmic rays in the heliosphere

The different types of cosmic ray particles and their role in the heliosphere are briefly described. The rates of various energetic particles were examined as a function of time and used to derive various differential energy gradients. The Pioneer and Voyager cosmic ray observations throughout the heliosphere are indeed giving a perspective on the three-dimensional character and size of the heliosphere. Most clearly the observations are emphasizing the role that transient variations in the outer heliosphere, and most likely the heliospheric boundary shock, play in the 11 year solar cycle modulation of cosmic rays.

Webber, William R.↗
NASA NTRS1986

Effects of three-dimensional heliospheric structures on cosmic-ray modulation

The theory of cosmic-ray transport in the heliosphere contains four distinct physical processes - diffusion, convection, adiabatic cooling, and drifts. The last of these has only recently been evaluated. Extrapolation of present understanding of the regions near the heliospheric equator to high heliographic latitudes leads to the conclusion that particle drift in the large-scale magnetic field plays an important role in cosmic-ray modulation. The large-scale, three-dimensional structure of the interplanetary magnetic field is therefore very important in understanding cosmic rays. Several key observed modulation effects are summarized, each of which is a natural consequence of drift, but which requires special assumptions if drift plays no role. It is concluded that particle drifts play an important and possibly dominant role in transport in the heliosphere.

Jokipii, J. R.↗
NASA NTRS1986

Measurement of radial and latitudinal gradients of cosmic ray intensity during the decreasing phase of sunspot cycle 21

The cosmic ray radial and latitudinal gradients during the 1981-1984 decreasing phase of sunspot cycle 21 are investigated based on data from Voyagers 1 and 2, with a detector threshold of not less than 70 MeV/nuc, and IMP-8, with a detector threshold of not less than 35 MeV/nuc. During the interval, the heliolongitudinal separation between the Voyager spacecraft changed from about 4 to 26 deg, and comparison of the 26-day means of the cosmic ray intensities obtained show that the data is consistent on the average with a long-term zero latitudinal gradient. Comparison at 1 AU of Voyager and IMP-8 data illustrate that the radial gradient decreased over this period at the rate of about 0.4 percent per AU per year, reaching a value of about 2.0 percent/AU between 16 and 22 AU, and a value of about 0.6 percent/AU between 16 and 22 AU, a pattern which would locate both Voyagers during 1977 outside the principal cosmic ray modulation at solar minimum within 22 AU.

Venkatesan, D.↗
NASA NTRS1986

He-3 in galactic cosmic rays

Cosmic-ray He-3/He-4 observations, including a new measurement around 65 MeV per nucleon from ISEE-3, are compared with interstellar propagation and solar modulation calculations in an effort to understand the origin of cosmic-ray He nuclei. A survey of spacecraft and balloon observations of the He-3/He-4 ratio shows improved consistency among measurements in the 50-300 MeV per nucleon energy range when a previously neglected contribution from atmospheric secondary He-3 is taken into account. These low-energy observations imply a mean escape length of 6-8 g/sq cm in the standard 'leaky box' model for cosmic-ray propagation in the Galaxy, a value consistent with that derived from studies of heavier nuclei. No evidence is found for an excess of low-energy He-3 such as that reported at high energies.

Mewaldt, R. A.↗
NASA NTRS1987

Ultra-high-energy cosmic rays in a galactic wind and its termination shock

Results are reported from numerical modeling of the acceleration and transport of ultra-high-energy cosmic rays in a galactic wind and its termination shock. A two-dimensional (azimuthally symmetric) wind and spiral magnetic field, with a spherical termination shock, where the velocity drops suddenly, is assumed. The time-dependent cosmic-ray transport equation, including all major transport effects is solved using an implicit finite-difference scheme. Particles are injected as the shock of low energy, and the subsequent evolution of the distribution function is followed. Iron nuclei are readily accelerated at the shock to energies up to 100 billion GeV, and protons to 10 billion GeV. A major effect aiding the acceleration of these particles is the spiral of the magnetic field carried out by the wind, caused by the rotation of the Galaxy, with the result that the shock is nearly normal over most of its area. Increasing the magnetic field or rotation rate increases the maximum energy attainable. Anisotropies and energy densities of the particles are also discussed. It is concluded that the process is consistent with observations of ultra-high-energy cosmic rays.

Jokipii, J. R.↗