Particle Acceleration at a Blunt Termination Shock

Nathan Schwadron (BU) Marty Lee (UNH)

Dave McComas (SwRI)

Particle Acceleration at a Blunt Termination Shock

Nathan Schwadron (BU) Marty Lee (UNH)

Dave McComas (SwRI)

Voyager 1 Reaches the TS – December 2004

Shocking ACR Spectra Outside TS

■ Stone et al., 2005

■Unexpected when the ACRs observed by V1 did not peak at the TS as had been so widely predicted■Continued to see the characteristic ACR “bump” at ~100 MeV caused by modulation

The Voyager ACR Paradox

■ V1 Proved that ACRs were not being accelerated by the TS at the time and location where it passed through● So where and how are they accelerated?● Are ACRs generated only at special, favored acceleration

regions on the shock?● Are they accelerated only at some times at any given shock

location?● Are we completely wrong and ACRs are accelerated by

some other means at some location further out, beyond the termination shock (e.g., Gloeckler and Fisk)?

■ Clearly show how little we really know about our local cosmic accelerator

■ Local observations beg the question of the global interaction

Magnetic Geometry at a Blunt TS

■ TS shape taken from Zank, 1999

Injection Problem

Chalov, ‘93

Chalov, ‘05

Injection at a Blunt Termination Shock

Simple Model with Blunt TS

Diffusive Drift Acceleration

Diffusive Drift Acceleration

Correlated ACRs & GCRs

■ Strong correlation shows GCRs and ACRs are moving to the nose from much farther out in the heliosheath

Summary

■ Shape Matters !!!■ Always knew that TS was blunt and not spherical, but

didn’t appreciate that the TS shape drives the macro-interaction● Many sketches, drawings, and even some simulations

● Explained precursor event anisotropies inside TS (Jokipii et al., 2004)

■ Flattening of the nose of the TS produces a macro-scale geometry that enables a simple, standard time-dependent acceleration of ACRs● Smaller θBN and lower injection energies away from nose

● Higher energy particles generated on flanks where magnetic field lines have pierced the TS for longer times

■ Real spectra vs location will depend on actual TS shape and detailed interactions