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Galactic Cosmic-Ray Anisotropies: Voyager 1 in the Local Interstellar Medium
Space Physics · Submitted 28 May 2019
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the heliopause.
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The abstract, sentence by sentence
Since crossing the heliopause on August 25, 2012, Voyager 1 observed reductions in galactic cosmic ray count rates caused by a time-varying depletion of particles with pitch angles near 90-deg, while intensities of particles with other pitch angles remain unchanged. Between late 2012 and mid-2017, three large-scale events occurred, lasting from ~100 to ~630 days. Omnidirectional and directional high-energy data from Voyager 1's Cosmic Ray Subsystem are used to report cosmic ray intensity variations. Omnidirectional (greater than ~20 MeV) proton-dominated measurements show up to a 3.8% intensity reduction. Bi-directional (greater than ~70 MeV) proton-dominated measurements taken from various spacecraft orientations provide insight about the depletion region's spatial properties. We characterize the anisotropy as a "notch" in an otherwise uniform pitch-angle distribution of varying depth and width centered about 90 degrees in pitch angle space. The notch averages 22-deg wide and 15% deep - signifying a depletion region that is broad and shallow. There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the heliopause.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Since crossing the heliopause on August 25, 2012, Voyager 1 observed reductions in galactic cosmic ray count rates caused by a time-varying depletion of particles with pitch angles near 90-deg, while intensities of particles with other pitch angles remain unchanged. | result 1.00 | 0.90 | 0.56 | asserted 1.00 |
| s1 | Between late 2012 and mid-2017, three large-scale events occurred, lasting from ~100 to ~630 days. | result 1.00 | 0.79 | 0.05 | asserted 1.00 |
| s2 | Omnidirectional and directional high-energy data from Voyager 1's Cosmic Ray Subsystem are used to report cosmic ray intensity variations. | method 0.91 | 0.90 | 0.04 | asserted 0.97 |
| s3 | Omnidirectional (greater than ~20 MeV) proton-dominated measurements show up to a 3.8% intensity reduction. | result 1.00 | 0.92 | 0.09 | asserted 1.00 |
| s4 | Bi-directional (greater than ~70 MeV) proton-dominated measurements taken from various spacecraft orientations provide insight about the depletion region's spatial properties. | method 0.90 | 0.86 | 0.05 | asserted 0.86 |
| s5 | We characterize the anisotropy as a "notch" in an otherwise uniform pitch-angle distribution of varying depth and width centered about 90 degrees in pitch angle space. | result 0.85 | 0.90 | 0.37 | asserted 0.99 |
| s6 | The notch averages 22-deg wide and 15% deep - signifying a depletion region that is broad and shallow. | result 0.96 | 0.92 | 0.21 | asserted 1.00 |
| s7 | There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the heliopause. | interpretation 1.00 | 0.71 | 0.50 | hedged possibility 1.00 |
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The paper
Original abstract
Since crossing the heliopause on August 25, 2012, Voyager 1 observed reductions in galactic cosmic ray count rates caused by a time-varying depletion of particles with pitch angles near 90-deg, while intensities of particles with other pitch angles remain unchanged. Between late 2012 and mid-2017, three large-scale events occurred, lasting from ~100 to ~630 days. Omnidirectional and directional high-energy data from Voyager 1's Cosmic Ray Subsystem are used to report cosmic ray intensity variations. Omnidirectional (greater than ~20 MeV) proton-dominated measurements show up to a 3.8% intensity reduction. Bi-directional (greater than ~70 MeV) proton-dominated measurements taken from various spacecraft orientations provide insight about the depletion region's spatial properties. We characterize the anisotropy as a "notch" in an otherwise uniform pitch-angle distribution of varying depth and width centered about 90 degrees in pitch angle space. The notch averages 22-deg wide and 15% deep - signifying a depletion region that is broad and shallow. There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the heliopause.
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