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Observational evidences of CR acceleration at shocks chung-ming ko institute of astronomy and department of physics, national central university, taiwan.

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Presentation on theme: "Observational evidences of CR acceleration at shocks chung-ming ko institute of astronomy and department of physics, national central university, taiwan."— Presentation transcript:

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) launchoutward directiontermination Shockheliopause Voyager 11997.09.05 35.55 o ecliptic latitude 260.78 o ecliptic longitude at 3.50 AU/year cross on 2006.12.16 at 94 AU expect to reach in 2015 Voyager 21997.08.20 47.46 o ecliptic latitude, 310.89 o ecliptic longitude at 3.13 AU/year could cross between 2008 and 2010 reach in 10 years after crossing TS

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

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

9 how do we know Voyager 1 have crossed the termination shock?  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 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 how about energetic particles?  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 Stone et al. 2005

12 TSPs  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 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 UV pickup by solar wind at around 1 KeV/nucleon then 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 ACR acceleration  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! Stone et al. 2005 further into heliosheath immediate upstream immediate downstream

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 interplanetary shocks

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

20 typical IP shock  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 Desai et al. 2003

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

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 seed population  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  3 He rich events associated with solar flares 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 ACE news #91, 2005.08.30 (Kallenbach & Bamert) Terasawa et al. 2006 2000.07.15 event (Bastile day event)

28 modified shock?  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?) Mewaldt et al. 2005

29 Terasawa et al. 2006 shock precursor? 1994.02.21 event2003.10.29 event (Halloween event)

30 complications  both 3 He and 4 He intensities are increased at CME magnetic compression region (C) and CME fast forward shock (S)  3 He/ 4 He 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 ACE news #44, 2000.04.25 (Desai et al.)

31 complications  2005.01.20 event pushes the shock model to its extreme parameters regime  because of the fast rise time and intensity 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  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 354 shocks

35  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) 162 fast forward IP shocks (CME related) ACE news #44, 2000.04.25 (Lario et al.)

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

37 the end

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