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Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations

● V-1. SHINE Nova Scotia, August 2009. ● V-2. Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations. J. K ό ta University of Arizona Tucson, AZ 85721-0092, USA Thanks: J.R. Jokipii, J. Giacalone. kota@lpl.arizona.edu. Difference between 1 & 2 D Shocks.

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Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations

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  1. ● V-1 SHINE Nova Scotia, August 2009 ● V-2 Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations J.Kόta University of Arizona Tucson, AZ 85721-0092, USA Thanks: J.R. Jokipii, J. Giacalone kota@lpl.arizona.edu

  2. Difference between 1 & 2 D Shocks ● Are Anomalous Cosmic Rays (ACRs) indeed accelerated at the solar wind termination shock (TS) ? Likelyyes but ● Bluntness of TS counts ● Topology between shock & field Lines counts (cannot be modeled in 1 D) ● Model still qualitative Do not consider other important effects, like dynamical variations

  3. Voyager-1 fooled us with (1) “anti-sunward” precursor anisotropiesSolution: field line intersects the TS multiple times. Multiple intersection explains precursor anisotropies and …. V-2 V-1 Displacement of the ‘nose’ helps

  4. Voyagers fooled us with(2) spectra did not unfold at crossing the TSSolution: field lines .….? ACR fluxes continued to increase into the Heliosheath ● Temporal variaton (Florinski Zank,2006) ● Magnetic topology (McComas & Schwadron, Kόta & Jokipii) ● Combination of the two? Can be a direct result of 2D topology Could have been foreseen (Kόta & Jokipii, 2004)

  5. McComas and Schwadron (2006) Blunt Shock Injection & Acceleration at Flanks Short time for acceleration Kóta and Jokipii, 2004

  6. 2D simulation of Blunt TS (offset circle)- no latitudinal motion - This Simulation: Shock & Injection stronger at nose, weaker toward tail More TSP at nose (injection profile) Less ACRs at nose (global feature)

  7. 2 D simulation (offset circle) cont’d Simulated spectrum unfolds gradually Nose-tail asymmetry Controlled by κ┴ ACR flux continues to increase beyond TS

  8. Tracing back ACRs • Solve Parker’s equation “backward”, with the solar wind blowing inward. What we obtain is the “chance” function which is to be convolved with injection. • Inward wind advects trajectories back to the TS, where pseudo-particles cool-down to injection energy. • Ideally suited for GCRs (all trajectories leave sooner ot later the heliosphere. More cumbersome for ACRs

  9. ”Backward tracing” starting w5 MeV ACR 10 AU off the TS 5 MeV Cooled down to 100 keV Starting energy 5 MeV

  10. Chance to become 5 MeV ACR10AU off the shock Real numbers acceleration cooling Nose (V-1) Flank 60 West

  11. Age distibution ACRs are `older’ deeper in the HS Nose & 60E Reverse method w larger κ Forward method w smaller κ

  12. Implications: • ACRs are best accelerated if injected at front (more time for acceleration) • Birthplace at Nose: Likely most of all ACRs (even those in tail) were injected at front. • Nursery toward Flanks: TSP seen by Voyagers is the seed population of MeV ACRs. TSPs moving toward flanks during further acceleration.

  13. One word on Precursor Events:Possible scenarios for Voyager • Scenario (M* ) is more efficient to accelerate energetic particles • Voyager precursor events may have been associated with configuration M* M* Less efficient- More efficient > <

  14. Summary: ●V-1 ●V-2 ● Magnetic field lines cross the blunt TS multiple times. This explains upstream anisotropies and : ● Two-population spectrum: ACRs start as TSPs at the nose and move toward the flanks during acceleration. Appear still modulated at the TS, and continue to increase into the heliosheath. ● 2-D Shock differs from 1-D shock (topology) ● Dependence on parameters (κ) still need to be explored .

  15. Global features are insensitive injection profile • The distribution & spectrum of MeV ACRs turn out largely insensitive to the injection-profile along the shock. • Lower ACR intensity is obtained at the nose even if - injection rate and/or shock ratio is higher at nose Reason: unfavourable topology (natural cold spot) • To trace the history of ACRs we perform a “backward“ simulation. The solar wind is reversed and a pseudo ‘testparticle’ is released from the point of observation. What we obtain is the Green-function or chance of injected particle to become ACR

  16. Illustrative example of 2-D shock- field/shock angle alternates - cold hot Along shock front “nose” “tail” Distance from shock Global structure along shock front organized by magnetic field

  17. Motivation: where is the source?is history repeating itself ?Do we need a new paradigm ? Likely not ACR fluxes continued to increase beyond TS Source outside Shock V. Hess 1912 Voyager-1 December 2004 Similar result from V-2 (2007)

  18. Global structure of Heliosphere VLISM: partially ionized H,He 0.1/cc μG B ? ACR SEP GCR

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