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