Low-energy Charged Particles at Voyagers 1 and 2 10-20 AU into the Heliosheath (Invited)

Details Low-energy Charged Particles at Voyagers 1 and 2 10-20 AU into the Heliosheath (Invited) Low-energy Charged Particles at Voyagers 1 and 2 10-20 AU into the Heliosheath (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh23d..02d&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH23D-02

Physics

Plasma Physics

[2114] Interplanetary Physics / Energetic Particles, [2124] Interplanetary Physics / Heliopause And Solar Wind Termination, [2152] Interplanetary Physics / Pickup Ions, [7845] Space Plasma Physics / Particle Acceleration

Scientific paper

Voyager 1 (115 AU, N34°) and Voyager 2 (93 AU, S29°) have been in the heliosheath since Dec. 2004 and Sep. 2007, respectively. Intensities of low-energy ions 40 keV - few MeV observed at Voyager 1 have been relatively steady since mid-2006. The heliosheath-averaged (5.6-year) Voyager 1 energy spectrum rolls over slightly with increasing energy, with the spectral index changing from -1.5 to -1.7. Intensities of ions 30 keV - few MeV observed at Voyager 2 have been relatively steady since about 2009.4, in contrast to the large quasi-recurrent variations observed from 2007.66 (termination shock) to 2009.4. The low-energy ion energy spectrum at Voyager 2 is slightly harder than that at Voyager 1. The Voyager 2 spectrum averaged over 2007.66-2009.4 shows a rollover, with the spectral index changing from -1.3 to -1.5. After about 2009.4 at Voyager 2, the lower energy ion channels show large anisotropies consistent with the observed direction of heliosheath plasma flow, but not with its speed. Preliminary analysis suggests that in addition to H+, these channels may also be measuring heavy ions, i.e., pickup He+ and/or O+ at energies >4 and >9 keV/nuc, respectively, that could be boosted into sunward viewing sectors of the detector by the ~150 km/s heliosheath flow. Intensities of energetic (0.02-1.5 MeV) heliosheath electrons began decreasing exponentially at Voyager 2 on 2009.15, and are now at detection background. Energetic electron intensities at Voyager 1 remain high. We estimate the heliosheath plasma flow velocity in the R-T (instrument scan) plane at Voyager 1 by using angular data from the three lowest energy ion channels that cover 40-139 keV. We cannot measure the component of flow normal to the R-T plane. During 2007.7-2010.5, the estimated radial component of flow decreased from ~60 km/s to ~0 km/s at a rate of -20 km/s/yr. On average, the tangential component of flow has been at about -40 km/s from termination shock crossing onward, but continues to show broad variations of ±20 km/s.

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