HR: 1340h
AN: SH14A-1694    [Abstracts]
TI: Diffusive Acceleration at the Blunt Termination Shock
AU: * Schwadron, N A
EM: nathanas@bu.edu
AF: Boston University, Dept of Astronomy 725 Commonwealth Ave, Boston, MA 02215, United States
AU: Lee, M
EM: marty.lee@unh.edu
AF: University of New Hampshire, Dept. of Physics, Morse Hall 39 College Road, Durham, NH 03824, United States
AU: McComas, D J
EM: dmccomas@swri.edu
AF: Southwest Research Institute, 6220 Culebra, San Antonio, TX 78238, United States
AB: Voyager 1's recent and long anticipated passage into the heliosheath contradicted the prediction that we would observe the source of anomalous cosmic rays accelerated by the termination shock. The observed energetic protons reveal a power-law spectrum below several MeV, but above several MeV the spectrum falls more sharply, and we observe the familiar bump caused by modulation of anomalous cosmic rays. Here, we develop the theoretical framework to include the motions and drift of particles during diffusive shock acceleration at a 3-D termination shock, including cross-field diffusion, and curvature and gradient drifts. Our model supports the concept of McComas and Schwadron that because of the termination shock's blunt structure, there should be a strong deficit of locally accelerated anomalous cosmic rays near the nose. With reasonable parameters for the scattering mean free path parallel to the magnetic field of ~3 AU, and a ratio of perpendicular to parallel diffusion of ~0.03, the model produces an energy spectrum that agrees well with Voyager 1 observations near the termination shock. These parameters also lead to an acceleration time to 10 MeV of about 1 year, which is comparable to previous estimates derived from the observed charge states of ACRs. Thus, we provide a theory for diffusive acceleration at the blunt termination shock. The predictions of this theory are consistent with Voyager 1's observations showing a lack of ACRs accelerated near the nose of the termination shock and the ACR acceleration timescale derived from ACR charge-states.
DE: 2104 Cosmic rays
DE: 2114 Energetic particles (7514)
DE: 2124 Heliopause and solar wind termination
DE: 2126 Heliosphere/interstellar medium interactions
DE: 7845 Particle acceleration
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting