1. Ion Acceleration Near CME-driven shocks Paper No. 84, SH1.3 ICRC 2011, Beijing, China Ion Acceleration Near CME-driven shocks Paper No. 84, SH1.3 ICRC 2011, Beijing, China Mihir I. Desai Southwest Research Institute University of Texas at San Antonio Co-authors: Maher A. Dayeh, Martin A. Lee, Charles W. Smith & Glenn M. Mason Mihir I. Desai Southwest Research Institute University of Texas at San Antonio Co-authors: Maher A. Dayeh, Martin A. Lee, Charles W. Smith & Glenn M. Mason

2. CME Shocks & Energetic Particles CMEs drive shocks in the corona and the interplanetary medium Coronal Shocks  SEPs IP shocks  ESPs Reames.SSR, 1999 ESP SEP

3. Datasets and Event Selection Started with ACE Shock list of ~400 IP shocks from August 1997 - December 2006 Removed 326 events with no intensity increases, multiple shock events, and irregular time-profiles (e.g., Lario et al. 2005) Hand-picked 10 of the remaining 74 events, combining energetic particle, magnetic field data, and shock normal angles Selected events on the basis of the evolution of the CNO spectral index, Fe/CNO ratio and the presence/absence of self-excited waves

4. Type 1: 1) CNO intensities increase by factor of ~10 2) CNO spectral index remains constant 3) Fe/CNO constant 4) A 1 reverses A 2 peaks at 90° Particles

5. Wave Properties Type 1: Magnetic power spectral density increases simultaneously at all frequencies No increase near pc

6. Type 2: 1)CNO intensities increase x 100 - lowest energies peak at shock 2) CNO spectrum: no change @510 keV/n, softens @40 keV/n 3) Fe/CNO ratio @60 keV/n decreases at shock 4) A 1 & A 2 zero Particles

7. Wave Properties Type 2: Upstream Region: Magnetic power spectral density increases dramatically between 0.01 - 0.5 Hz Bump around pc is due to waves excited by low-energy protons

8. Change in CNO Spectrum vs shock Normal Angle Softens for 5 events with θ BN <70° No change for 4 events θ BN >70° 1 σ

9. No wave activity upstream Shock shifts the intensities of the pre- event or seed spectrum at all energies simultaneously Significant deficit of low-energy CNO ions causes spectrum to “unfold” as the shock arrives closer to the S/C Significant wave excitation upstream CNO Spectral Evolution ~2 hr @ shock

10. Events with no wave activity – Quasi-perp Events with wave excitation; oblique shocks Implications for Source Populations Axford 1981, 17 th ICRC; Tylka et al., 2005; Lee 2005, CP 781 Lee, 1983

11. Decreases by > factor of 2 for 6 events with θ BN factor of 2 for 6 events with θ BN <70° No change for 4 events with θ BN >70° Change in Fe/CNO vs θ Bn 1 σ

12. Fe/O ratio Fe/O at 6 IP shocks with wave excitation shows strong evidence of M/Q-dependent acceleration processes Desai et al., 2003, ApJ, vol.588, 1149 Fe: M/Q ~ 4.5 O: M/Q ~ 2.3 Fe accelerated less efficiently than O

13. Conclusions 64 of 74 IP shocks exhibit “mixed” signatures with pre-accelerated, suprathermal-energetic ions as seed particles64 of 74 IP shocks exhibit “mixed” signatures with pre-accelerated, suprathermal-energetic ions as seed particles Studied 10 events with clear signatures of either shock-drift or first-order Fermi accelerationStudied 10 events with clear signatures of either shock-drift or first-order Fermi acceleration Type IType II 4 Quasi-perp IP shocks with no wave excitation  Shock-drift acceleration of pre-accelerated energetic ions; Spectral index and Fe/CNO abundance in seed population are preserved 6 oblique shocks with significant wave excitation  Fermi acceleration with waves excited by low-energy protons; Fe/CNO shows strong evidence of M/Q-dependent acceleration mechanisms

14. Results Summary Particle/Wave/ Shock Property Type I (4 events)Type II (6 events) CNO spectrum @40 keV/n @510 keV/n No change at shock Softens below 300 keV/n.; No change above 300 keV/n. Fe/CNO ratio @60 keV/n No change at shockDecreases by > factor of 2 at shock AnisotropiesA 1 reverses or zero A 2 peaks @ 90° or zero A 1 reverses or zero A 2 zero Shock Normal Angle Quasi-Perp (θ BN >70°)Oblique (θ BN <70°) Wave Excitation No increase near pc Increases in 0.001 - 0.8 Hz range @ pc

15. No wave excitation upstream Significant wave excitation upstream Another 2 examples in our study Shock shifts the pre-event spectrum upward in intensity and energy Significant deficit of low-energy CNO ions causes spectrum to “unfold” as the shock gets closer

16. Quasi-perp shocks, Lee 2005 ~0.5 MeV/nucleon O spectra correlated with ambient ST indices  Reacceleration of ST seed spectra Desai et al., 2004, ApJ, vol. 611, 1156. Axford 1981, 17 th ICRC Tylka et al., 2005 Lee 2005, CP 781

17. Ion Spectrum, softens at shock Far upstream - very few low energy particles can escape Intensity increases localized near shock Accelerated protons excite upstream waves that resonate with and trap lower-energy ions near the shock Significant wave excitation upstream Oblique/Quasi-par. shocks, Lee 1983 Wave intensity increases around the proton cyclotron frequency i.e., near pc

18. Backup Slides

19. Shock Acceleration Mechanisms Quasi- Perp Shock  Shock drift; Quasi- Parallel Shock  Diffusive shock accelerati onp  Bn >60º  Bn <60º

21. Change in CNO Spectrum vs shock speed No clear relationship between change in CNO spectral index and shock speed 1 σ

22. Softens for 5 events: V SH sec( θ BN )<1000 km/s No change for 4 events: V SH sec( θ BN )>700 km/s V SH sec( θ BN ) = injection threshold speed Change in CNO Spectrum vs shock speed along upstream B 1 σ

23. Wave Excitation near IP Shocks Case studies of ESP eventsReferenceSeed Population 0.03-1.6 MeV protons upstream waves 0.03-0.3 Hz ISEE-3 - Nov.12, 1978 Kennel et al. (JGR, 1986) Gordon et al. (JGR, 1999) SW ions 0.06-2 MeV proton spectra, upstream waves between ~0.25-3 mHz ACE/SoHO - Bastille Day & Halloween Events Bamert et al. (ApJ, 2004) Kallenbach et al. (AIP CP 781, 2005) ~1 MeV SEP ions 0.05-0.3 MeV ions; upstream waves between ~0.01-0.1 Hz; ACE: DOY 295, 2003 Lario et al. (AIP CP 781, 2005) 1-100 keV ions, Composition not like SW ~50-600 keV protons; upstream waves between ~0.01-0.4 Hz; ACE: DOY 224, 2000 Smith et al. (AIP CP 781, 2005) “colder” ions in presence of a “sea” of hot SEP background

24. Tylka et al., ApJ 2005 SAMPEX: Labrador et al. (2003) Mazur, private communication. TTM: Dietrich & Tylka 2003 ST seeds & θ Bn  Multiple seed populations  Shock geometry is critical  Produces increasing Fe/O with energy and positive correlation of high Q state and Fe/O

25. #Spectral IndexShock Normal Upstream Waves, Frequency RangeEvent Type 1*No Change80.3 ± 1.2NoI 2Softens30.5 ± 13.9Yes, 0.01 - 1 HzII 3*Softens51.6 ± 2.8Yes, 0.01 - 0.5 HzII 4No Change79.3 ± 8.8Yes, 0.02 - 0.5 HzMixed 5Softens70.3 ± 6.3NoMixed 6No Change86.5 ± 7.7NoI 7Softens70 ± 2.2Yes, 0.001 - 0.5 HzII 8No Change88 ± 7.4NoMixed 9No Change87.5 ± 3.4Yes, 0.001 - 0.2 HzMixed 10No Change79 ± 3NoI 11Softens23 ± 8Yes, 0.005 - 0.5 HzII 12No Change35.3 ± 11.6Yes, 0.008 - 0.5 HzMixed 13Softens42.8 ± 3.9Yes, 0.02 - 0.8 HzII 14No Change74.8 ± 4.3NoI 15No Change75.2 ± 5Not Yet Analyzed? 16Softens76.3 ± 13.9NoMixed 17Softens38.6 ± 6.3NoMixed Events Summary

26. Wave power increases between 0.03-0.3 Hz range, i.e., near pc A Test Case (Kennel et al. 1986) Kennel et al., 1986 Gordon et al. (JGR, 1999); Spectrum softens at shock due to arrival of low-energy ions Protons 112-157 keV Protons 30-36 keV Protons 308-475 keV

27. New Picture for Seed Particles for CME- driven shocks Image Credit: ILWS Sentinels Science Definition Team Report Suprathermal material (from flares, pick-up ions, gradual SEPs, SW) provide much of the seed population for CME shocks (Mewaldt et al., 2001)

28. Re-acceleration of Seed Spectra