Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh23c..01c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH23C-01
Physics
[2104] Interplanetary Physics / Cosmic Rays, [2124] Interplanetary Physics / Heliopause And Solar Wind Termination, [2152] Interplanetary Physics / Pickup Ions
Scientific paper
Both Voyager spacecraft are now in the heliosheath and observing several populations of energetic particles. At the lowest energies, there is a population, which we refer to as Termination Shock Particles (TSPs), which we attribute to local acceleration at the termination shock in the vicinity of where the spacecraft crossed it. At Voyager 1 (V1), this population has been very steady for the last four years, since about a year after shock crossing. At Voyager 2 (V2), the TSP spectrum has been variable, particularly at energies of a few MeV, for about 1.5 years since the shock crossing in August-September 2007. Recently, the variations have become smaller and the intensity vs. time profiles resemble those at V1. At mid-energies, the anomalous cosmic ray (ACR) energy spectra continue to evolve, responding to decreasing solar modulation and to motion through a spatial gradient. The ACR source must be beyond the position of V1 and could be near the heliopause or on the termination shock somewhere other than where V1 and V2 crossed it. At the highest energies, galactic cosmic ray (GCR) ions appear to have a very small spatial gradient. Since the measured GCR ion intensities are well below the intensities thought to be present just outside the heliosphere, there may be a region of enhanced modulation beyond V1. We will report the latest observations of these particle populations in order to better understand their source and propagation characteristics. This work was supported by NASA under contract NAS7-0301.
Cummings Alan C.
Heikkila Bryant C.
Lal Niranjan
McDonald Frank B.
Stone Edward C.
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