Low-energy Ions and Electrons Measured at Voyager 2 in the Heliosheath

Details Low-energy Ions and Electrons Measured at Voyager 2 in the Heliosheath Low-energy Ions and Electrons Measured at Voyager 2 in the Heliosheath

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsh31b..02d&link_type=abstract

American Geophysical Union, Spring Meeting 2008, abstract #SH31B-02

Physics

2104 Cosmic Rays, 2114 Energetic Particles (7514), 2124 Heliopause And Solar Wind Termination, 2139 Interplanetary Shocks, 2152 Pickup Ions

Scientific paper

Voyager 2 (85.3 AU, S28° lat.) is in the inner heliosheath downstream of the solar wind termination shock, having crossed the shock at 83.7 AU several times during days 242-244 of 2007 under relatively quiet solar wind conditions. Large fluctuations in intensities of heliosheath ions, particularly those with energies below ~0.2-0.3 MeV, measured throughout the past 185 days suggest that Voyager 2 remains near the shock. This differs from the situation at Voyager 1, which was evidently left several AU behind the termination shock that moved rapidly sunward over the spacecraft at 94 AU in late 2004, and this difference may help us to separate injection and/or acceleration processes associated with the shock from those associated with the turbulent heliosheath. For example, energy spectra of low-energy heliosheath ions differ at the two spacecraft. When averaged over the first one-third year period behind the termination shock, Voyager 2 energy spectra of ions 0.03- 3.5 MeV are well fit by a single power-law with index -1.25 ± 0.05, while Voyager 1 energy spectra of ions 0.04-4.0 MeV are well fit by a single power-law with index -1.67 ± 0.03 (which later increased somewhat to - 1.4 to-1.6). In more recent Voyager 2 data taken during 2008, the ion spectrum steepens with increasing energy, with the spectral index decreasing from ~-1.2 at 0.03 MeV to ~-1.7 at 3.5 MeV. The high intensities of these suprathermal heliosheath ions and their relatively hard energy spectra produce high ion partial pressures that may often dominate those associated with the thermal plasma and magnetic field, indicating that suprathermal ions may play a major role in dynamical processes occurring at the termination shock and in the heliosheath. We also discuss 0.02-1.5 MeV electron intensity increases measured in association with the termination shock crossing and electron energy spectral variations measured in the heliosheath.

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