The Voyager Cosmic Ray Experiment

Stilwell, D. E.; Davis, W. D.; Joyce, Robert M.; McDonald, F. B.; Trainor, J. H.; Althouse, W. E.; Cummings, A. C.; Garrard, T. L.; Stone, E. C.; Vogt, R. E.

doi:10.1109/tns.1979.4329683

Cited by 16 publications

(5 citation statements)

References 4 publications

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“…Upon further examination of the CRS cosmic-ray data, we discovered that the electron plasma oscillation events are consistently preceded by small bursts in the counting rates of electrons from the Electron Telescope (TET) of the CRS, a telescope which was specifically designed to detect 3 MeV electrons (Stilwell et al 1979). An example of one such burst is illustrated in Figure 4, which shows a series of expanded timescale plots for the 2014 February-November electron plasma oscillation event.…”

Section: Cosmic-ray Precursorsmentioning

confidence: 99%

A Foreshock Model for Interstellar Shocks of Solar Origin: Voyager 1 and 2 Observations

Gurnett

Kurth

Stone

et al. 2020

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The Voyager 1(V1) and Voyager 2(V2) spacecraft were launched in 1977 on a mission to explore the outer planets and reach the heliopause, the boundary between the hot solar plasma and the relatively cool interstellar plasma. V1 reached the heliopause on 2012 August 25, at 121.6 au, and V2 reached the heliopause on 2018 November 5, at 119.0 au. One of their remarkable discoveries was the detection of shocks propagating into the interstellar plasma from energetic solar events. These shocks are typically preceded by electron plasma oscillations excited by electron beams streaming along interstellar magnetic field lines ahead of the shocks. The frequencies of the plasma oscillations have now provided radial electron density profiles in the outer heliosphere and in the interstellar medium to radial distances of more than 145 au. The oscillations are typically preceded by bursts of high-energy ∼5-100 MeV electrons. These electron bursts are interpreted as being due to the reflection (and acceleration) of cosmic-ray electrons by the shock at the time the shock first contacts the magnetic field line that passes through the spacecraft. Relative timing between the cosmic rays reflected by the shock and the onset of the plasma oscillations allow us, for the first time, to estimate the energy, ∼20-100 eV, of the electron beams responsible for the plasma oscillations. These observations are combined into a self-consistent model called the foreshock model that describes the interaction of shocks of solar origin with the interstellar plasma.

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Section: Cosmic-ray Precursorsmentioning

confidence: 99%

A Foreshock Model for Interstellar Shocks of Solar Origin: Voyager 1 and 2 Observations

Gurnett

Kurth

Stone

et al. 2020

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“…Critical for evaluating the presence of JCRPs are observations near and within Jupiter's magnetosphere, which can inform us about the efficiency proton and ion acceleration in that system and what the spectrum of the particles escaping into the heliosphere is. The search for very high energy protons and heavy ions through measurements near Jupiter by Voyager (Krimigis et al 1977;Stilwell et al 1979), Ulysses (Simpson et al 1992), Juno (Mauk et al 2013;Becker et al 2017), and Galileo (Garrard et al 1992;Williams et al 1992) could constrain the spectrum of possible JCRPs escaping from the planet's magnetosphere and allow for a comparison with observations at different heliocentric distances, similar to Vogt et al (2018). Within the Jovian magnetosphere, protons and ions between several MeV n -1 and up to ∼100 MeV n -1 have been observed in the planet's radiation belts, at an acceleration region in Jupiter's middle and outer magnetosphere, or on highlatitude field lines possibly mapping to the auroral region (Zhang et al 1995;Fischer et al 1996;Anglin et al 1997;Selesnick et al (2001).…”

Section: Tablementioning

confidence: 99%

Jovian Cosmic-Ray Protons in the Heliosphere: Constraints by Cassini Observations

Roussos

Krupp

Dialynas

et al. 2019

ApJ

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Measurements of >82 MeV Galactic cosmic-ray (GCR) protons at Earth indicate that they may be mixed with protons that leak into the heliosphere from Jupiter's magnetosphere (Jovian cosmic-ray protons (JCRPs)). A ∼400 day periodicity in these proton fluxes, which is similar to the synodic period between Jupiter and Earth, and an excess proton flux observed when Jupiter and Earth can be connected through the interplanetary magnetic field were the basis for this claim. Using nearly 13 yr of GCR measurements at Saturn with Cassini's Magnetosphere Imaging Instrument, we show that the ∼400 day periodicity is also present in 100 MeV protons at ∼9.6 au, although the synodic period between Saturn and Jupiter is ∼20 yr. We also find that the features responsible for this periodicity were convected from 1 au to Saturn's distance with the solar wind velocity. Their origin is therefore heliospheric, not Jovian. We attribute these features to quasi-biennial oscillations, observed in the solar magnetic field and various heliospheric indices. This finding indicates that fluxes of JCRPs at 1 au, if present, are considerably overestimated, because the signal originally attributed to them represents the amplitude of the ∼400 day periodic GCR oscillation. This oscillation has to be subtracted before the resulting proton GCR flux residuals are analyzed in the context of a possible Jovian source. A confirmation of the presence of JCRPs over extended regions in the heliosphere and a constraint on their fractional abundance in GCR spectra may therefore require further validation and analysis, and several options are proposed for this purpose.

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“…The isotope telescopes have very large geometric factors of 44 cm2 sr for the HI, and of 58 cm2 sr in total for the MI, covering the broad energy range of 3.0-230 MeV/n. The telescopes so far aboard the IMP-8/9 (Garcia-Munoz et al, 1977), ISEE-3 (Althouse et al, 1978;Greiner et al, 1978) and Voyager-1/2 (von Rosenvinge et al,1978;Stone et al, 1.977;Stilwell et al, 1979) spacecraft launched in the 1970s, have the geometric factors of about a few cm2 sr or less. The GEOTAIL observes energetic ions in the period from the declining phase to the minimum of solar activity.…”

Section: Initial Results Of Hi/mi Spectrometersmentioning

confidence: 99%