Voyager Observations of Cosmic Rays in the Heliosheath

Details Voyager Observations of Cosmic Rays in the Heliosheath Voyager Observations of Cosmic Rays in the Heliosheath

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh13c..05m&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH13C-05

Physics

[2100] Interplanetary Physics, [2104] Interplanetary Physics / Cosmic Rays

Scientific paper

Since crossing the termination shock in 2004.95 (94AU 36°N), Voyager 1 has penetrated some 24 AU into the heliosheath over a period that now extends from near solar maximum conditions to the onset of the cycle 24 modulation at 1AU in ~ 2010. Voyager 2 entered the heliosheath in 2007.66 (83.7 AU, 27.5°S). Over the period 2006.0-2011.5 the V1/V2 265MeV/n galactic cosmic ray (GCR) He has increased at an average rate of 6.3% /year with an instanteous radial gradient of 0.2 ± 0.2%/AU. The rate of increase of 265 MeV/n H is 14%/year and 10 MeV GCR electrons increased at 55%/year. While the GCR intensities were increasing, the 15 MeV/n and 43 MeV/n ACR He at V1 began a slow decrease in 2009 that is becoming moderately steeper with time suggesting the spacecraft may be entering the region of higher magnetic fields expected near the heliopause. In 2011 the V1 GCR carbon spectra between 20 and 80 MeV/n has a slope of 1 as would be expected if the heliosheath functions as a long term storage region for GCRs with occasional forays into the region of the supersonic solar wind where they experience adiabatic energy losses. An alternate interpretation would be that their low-energy local interstellar spectrum is quite different from what was expected. Heliosheath transient increases are observed at the Voyagers, generally involving GCR ions and electrons and ACRs and which can persist for almost a year. The trigger for these events is not known at this time. The Voyager observations are establishing that at energies below ~ 1 GeV, the heliosheath is a vital, complex part of the cosmic ray dynamics in our solar system.

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