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observational evidences of CR acceleration at shocks

observational evidences of CR acceleration at shocks. chung-ming ko institute of astronomy and department of physics, national central university, taiwan. KAW4, KASI, Daejeon, Korea, 2006.05.17. shocks, shocks everywhere.

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observational evidences of CR acceleration at shocks

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  1. observational evidences of CR acceleration at shocks chung-ming ko institute of astronomy and department of physics, national central university, taiwan KAW4, KASI, Daejeon, Korea, 2006.05.17

  2. shocks, shocks everywhere from interplanetary shocks to stellar wind termination shocks to supernova remnant shocks to merger shocks to …

  3. what I want to talk • SNR shocks has been discussed by Peter and Aya • DSA has been discussed by Hyesung • those are the things I know better than what I am going to discuss, so bear with me if I say something trivial or stupid • I will concentrate on heliospheric shocks • the particles are low energy (low energy energetic particles?), in MeV or even sub-MeV range

  4. interplanetary or heliospheric shocks (collisionless) • CME driven shocks • planetary and cometary bow shocks • CIR and MIR • termination shock • … • in situ measurements • energy spectrum • composition • temporal variation • magnetic field • Waves • plasma properties • seed • …

  5. Voyager 1 has crossed the solar termination shock

  6. Voyager 1 & 2 (Voyager Interstellar Mission,VIM)

  7. voyage to the edge of heliosphere counterclockwise from top right Frisch et al. APOD20020624 Fisk (2005) Decker et al. (2005) APOD20020624

  8. heliosphere is just one more bubble in the sky but smaller bow shock near young star wind bubble from hot star planetary nebula

  9. magnetic field strength and its fluctuations 3 times increase in magnitude right across the shock field in heliosheath is 2.4 times the average upstream field larger fluctuations after shock crossing how do we know Voyager 1 have crossed the termination shock? Burlaga et al. 2005

  10. together with • abrupt increase in low-energy particle intensity • electron plasma oscillations • detected upstream and not detectable downstream • inferred solar wind speed • reduce solar wind speed Fisk 2005; Stone et al. 2005; Decker et al. 2005; Gurnett & Kurth 2005; Burlaga et al. 2005 termination shock (TS) is a reverse quasi-perpendicular pickup ion-dominated shock now it is at 94 AU and is moving inward (> 90 km s-1?) compression ratio: between 2.4 and 3.0

  11. besides SEPs, ACRs, GCRs there are TSPs recently TSPs are energetic termination shock particles (e.g., protons at several MeV) strongly affected by heliospheric disturbances such as MIRs how about energetic particles? Stone et al. 2005

  12. mysterious streaming outward along B field upstream of TS source located several AU closer to the sun and closer to the pole than Voyager 1 TS distorted by LISM B field or interstellar wind TSPs Decker et al. 2005

  13. TSPs before and after TS • upstream • field-align beaming • large intensity variation • large spectral slope variation (-1 to -2) • heliosheath • reduced anisotropy • less intensity variation • less spectral slope variation (-1.26 to -1.56) • spectral break varies very little (~ 3.5 MeV) • same source for upstream and heliosheath (steady source from TS) • reason of break unknown (cf., spectral break in ACR comes from adiabatic deceleration)

  14. ACRs • anomalous CRs are • interstellar neutrals ionized by UVpickup by solar wind at around 1 KeV/nucleonthen accelerated by TS to > 10 MeV/nucleon • ACRs are substantially modulated in the heliosheath • source is somewhere beyond (may still be TS but at a distance from the region where Voyager 1 crossed) Stone et al. 2005

  15. ACR spectrum • diffusive shock acceleration is alright • however, 0.04~20 MeV can also be explained by solar wind ram pressure heating at TS(Gloecker et al. 2005) Decker et al. 2005

  16. not quite what is expected the spectrum does not change and the intensity does not increase cross the shock low energy ions (< 3 MeV per nucleon) are rapidly accelerated, while high energy ions are not affected by shock TS is a shock but not an efficient accelerator new physics is needed?some say yes and some say no, of course! ACR acceleration further into heliosheath immediate downstream Stone et al. 2005 immediate upstream

  17. TSPs and ACRs • both ACRs and TSPs are accelerated pickup ions (e.g., both are deficient in carbon ions) • two stagess acceleration: first accelerate TSPs, then accelerate ACRs later (but further fractionation of H is needed in the second stage as H/He ratios are different) Stone et al. 2005

  18. interplanetaryshocks

  19. connection to earth magnetic field energized particles adapted from Lee 1983

  20. most interplanetary shocks are CME driven shocks in situ measurements by ACE, SOHO, WIND, Ulysess, Voyagers, IMP8, ISEE3, Goes, etc. particles are energized, but: seed population? location? self-excited waves? modified-shock? … ACE measurements 2000.06.20~2000.06.26 typical IP shock Desai et al. 2003

  21. SEPs (solar energetic particles) two types: gradual and impulsivedifferent isotopic compositions associated with CMEs? associated with flares? Reames 1999

  22. spectrum from solar wind to CR energies seed? high energy tail of solar wind? or pre-accelerated suprathermal ions? Mewaldt et al. 2001

  23. solar wind ions or suprathermal ions? observation of IP shocks at 1 AU indicates seeds come from suprathermal ions pre-accelerated by solar flares or other IP shocks 3He rich events associated with solar flares seed population Desai et al. 2003

  24. acceleration sites for SEPs • solar flares or CME driven shocks • common view (but not all) is CME driven shocks • how do we know • timing • spectrum and intensity of anisotropic ground-level events (GLEs) • GLE-associated with CMEs • solar gamma ray line flares has little correlation with SEPs • …

  25. self-excited waves • the idea is waves excited upstream of the shock by energetic particles trap the particles for further acceleration • the breaks in these spectra may be an indication of proton-excited Alfven waves (e.g., due to saturation) Mewaldt et al. 2005

  26. direct measurement • Bastille 2000 event (2000.07.15) • self-excited Alfven waves by protons • weakly super-Alfvenic ions generates ion whistler waves • ions are trapped by these waves near shock and thus increasing the efficiency of shock acceleration

  27. 2000.07.15 event (Bastile day event) Terasawa et al. 2006 ACE news #91, 2005.08.30 (Kallenbach & Bamert)

  28. at strong shock, when accelerated particles gain enough energy, backreaction will take place SEPs suck up ~10% of CME’s energy (dissipation of CME, modified shock?) modified shock? Mewaldt et al. 2005

  29. 1994.02.21 event 2003.10.29 event (Halloween event) Terasawa et al. 2006 shock precursor?

  30. both 3He and 4He intensities are increased at CME magnetic compression region (C) and CME fast forward shock (S) 3He/4He enhancement with respect to solar wind ion intensities at (C) is larger than at (S) indicates shocks are not the only acceleration mechanism in interplanetary space complications ACE news #44, 2000.04.25 (Desai et al.)

  31. 2005.01.20 event pushes the shock model to its extreme parameters regime because of the fast rise time and intensity complications Ryan et al. 2005

  32. factors affecting IP shock acc • shock strength, velocity, size and curvature, lifetime, etc. • quasi-parallel and quasi-perpendicular • seed populations • solar wind suprathermal • solar flare suprathermal • CMEs may or may not have associated shocks • direction of CMEs propagation and connectivity • … • a lot of things needs to be disentangled

  33. complicated business Mason 2001

  34. some statistics 354 shocks • how does energetic particle relate to shock parameter? • no apparent trend from shock angle and speed (except maybe shock speed has to be large enough for large increase in intensity) Cohen et al. 2005

  35. 162 fast forward IP shocks (CME related) • shock parameters may not govern the associated energetic particle event • maybe the energetic particle event is a history of injections and accelerations (by other shocks or accelerators), while the shock is measured locally • about half of the shocks do not affect pre-existing particle intensities, i.e., no shock acceleration (even for a few strong shocks) ACE news #44, 2000.04.25 (Lario et al.)

  36. it’s goodstill lots of things to do are you hungry for some? to be cont’d

  37. the end

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