WG7: Particle acceleration and transport

1. WG7: Particle acceleration and transport

2. Regular Participants

3. Our Goal • Topic I: Signatures of particle acceleration before (pre-event), during (impulsive phase) and long after the flare. • Topic II: Observational constraints on accelerated particles (energetics, numbers of accelerated particles, spectral-index evolution, location and acceleration time). • Topic III: Is the role of magnetic topology important for the acceleration and transport of high energy particles? • Topic IV: What is the respective role of shocks, stochastic acceleration and direct E-fields on particle acceleration, with emphasis on the their interrelation to the energy release process (reconnection). • Topic V: To what extend do the limitations to our current observations determine the processes involved? Such observational limitations include not only size-scale issues (both on sub-resolution and large size scales) but also energy regimes to which observational access is difficult (nonthermal electrons at low energies in the presence of thermal plasma and ions below ~5MeV). Although the properties of these particles are virtually unobserved, they may still play a major role in the energetics and the energy release.

4. Characteristics of Particle accelerator in the sun • Theme 1: The energy distribution of the accelerated particles and its evolution in time (Brown, Kontar, Massone, Piana, Lin, Share, Vilmer) • Problems: Direct way: accelerated particles transport on known magnetic topologies photons • Inverse process: Photons particle distribution

5. Mean Electron Spectrum: Temporal evolution (Kontar) 1 3 5 RHESSI Lightcurves 3-12keV; 12-25keV; 25-50keV; 50-300keV 2 4 Temporal evolution of the Regularized Mean Electron Spectrum (20s time intervals) 3 1 2 4 5

6. Accelerated (injected) Electron Spectrum(Kontar) Accelerated (injected) electron spectrum for a thick-target model: Temporal evolution of the Regularized Accelerated Electron Spectrum (20s time intervals) 3 1 2 4 5

7. Electron spectrum at 1AU Typical electron spectrum can be fitted with broken power law: Break around: 30-100 keV Steeper at higher energies Oakley, Krucker, & Lin 2004

8. Solar energetic particles at 1AU (Krucker-Kontar)

9. Evidence for Electron Spectral Hardening (Share)

10. Characteristics of Particle accelerator in the sun • Theme 2: Very high energy particle (Vilmer)

11. -ray and neutron event on 24/05/90 (Vilmer) From Talon et al., 1993 Debrunner et al 1997 High Energy -rays Solar neutrons PHEBUS/GRANAT observations Deduced solar neutron production time profile (i.e. pion time profile) NM CLIMAX observations of solar neutrons and prediction for a time extended neutron production Spectral evolution of high-energy -rays

12. Background subtracted count spectra From PHEBUS/GRANAT Full line: one of the best fits with electron and pion contributions Dotted line: electron contribution -ray lines Background subtracted count spectrum From 300 keV to 100 MeV Full line: one of the best fits with one electron bremsstrahlung component & pion contribution Dotted line: electron component Electron bremsstrahlung component: Ae= 1 10 5 = 2 Eroll= 40 MeV Proton component: =2 Ntot= 8 1031 Emax= 750 MeV Vilmer et al, 2003

13. Characteristics of Particle accelerator in the sun • Theme 3: Anisotropies • (Alexander, McConnell, Bastian)

14. Asymmetric footpoints (Alexander) I1 F1 F2 Following AM02 we define the footpoint photon asymmetry as where Ii denotes the count rate at footpoint i. For perfect symmetry A = 0 and for perfect asymmetry A = ±1.

15. X-ray Polarization studies • First analysis includes four events : • 1) 23-July-2002 • 2) 21-April-2002 • 3) 03-November-2003 • 4) 10-November-2004 • Only the July 23rd event shows evidence of polarization (at the 20% level in the 20-40 keV energy range). • Polarization angle not consistent with beamed emission at footpoint. Perhaps beamed emission with looptop source?!? Or pancake distribution at footpoint?!? (McConnell)

16. Characteristics of Particle accelerator in the sun • Theme 4: How many particles are accelerated? Estimates with the current modeling suggest that: The rate of particle acceleration is • so for atypical flare 1039 particle should be accelerated • Typical volume for a loop 1028 cm3 and density 1010 /cm3 In secs all particles of the loop should be accelerated and the loop should be refiled ten times. For the CS the situation is much worst….Possible Solution Evaporation of heated plasma + return current heating (Gordovskyy and Zharkova)

17. Characteristics of Particle accelerator in the sun • Theme 5: Magnetic topology (S. White, Alexander) and its role on acceleration and transport… • Complexity vs simplicity

18. Flare in which Fe XII shows a simple arcade late in the event and HXR come from top of arcade as in Y-type reconnection: but radio emission shows very complex structure early on. In this flare geometry evolved from complex to simple:not consistent with standard arcade reconnection model. (S. White)

19. Flare in which Fe XII and HXR come from a small location at front of the region while synchrotron-loop and 1600 A continuum come from very distant location: requires a very complex magnetic geometry with long-distance connections. Where was the energy release? (S. White)

20. Characteristics of Particle accelerator in the sun • Theme 5: Time delays and time of flight measurements (Aschwanden) • Generally, the HXR pulses or fine structure show TOF delays, • While the lowpass-filtered flux shows delays of opposite sign (trapping)

21. 50- 180 keV Time delays in g-ray line emission can be as small as <2 sec to as large as 10’s of sec. g-ray line emission in 2002 July 23 flare may be delayed by ~10 sec from hard X-rays. What does this say about acceleration-transport? Could be accounted for by trapping or is it intrinsic to the acceleration process? (Share) 275- 325 keV 4 – 6.4 MeV |-----20 sec----| 50- 180 keV 275- 325 keV 4 – 6.4 MeV |------100 sec------|

22. Characteristics of Particle accelerator in the sun • Theme 6: Energetic: Almost 30-50% of the energy released goes to high energy particles • Question: Is the flare process MHD or kinetic phenomenon?

23. Characteristics of Particle accelerator in the sun • Theme 7: Helium and Heavy ion acceleration • Theme 8: Long lasting acceleration (hours after the flare (Vilmer, Dauphin) • Theme 9: Supper hot tail in the solar wind withought a flares

24. Core => solar wind plasma electrons Halo/Strahl => heat flux from ~106 K corona Superhalo => remnant from coronal heating or solar wind acceleration? (Lin) Solar Wind Electrons

25. Can the existing flare models satisfy all the above constrains? • The only model that can satisfy only a few of the above constrains is the stochastic acceleration model but has no connection to energy release

26. The Big Questions • Are the existing models for particle acceleration connected with the energy release in solar flares? - NO! • Is there any model which satisfy all the above constrains? ---NO

27. Theoretical ideas • Acceleration of particles inside stressed magnetic loop(Turkmani) • PARTICLE ENERGY SPECTRA AT ACCELERATION IN an RCS WITH a GUIDING FIELD(Zharkova) • Evidence for particle acceleration at the termination shock(Warmuth) • Acceleration of particles in force free extrapolated magnetic fields(Azner-Vlahos)

28. Acceleration model (Turkmani) Acceleration takes place in stochastic current sheets’ regions developed as a result of the dynamic which the photospheric driving introduces to the corona.

29. Macroscopic description (MHD) (Galsgaard) • Flow velocities well below the speed of light • Length scales much longer than any free mean path of particles • Time scales much longer than giro frequency

30. The loop model (Galsgaard) • 3D MHD experiment of photospherically driven slender magnetic flux tubes • Continued random driving of the foot points (incompressible sinusoidal large scale shear motions ) • Reconnection jets generate secondary perturbations in B • Formation of stochastic current sheets

31. Electric field E = -(u x B) + J Inductive Resistive

32. Time evolution andDistribution functions (Turkmani)

33. Accepted current sheet scheme (Zaharkova)

34. Energy spectra: e (blue) and p (black)upper panel – neutral, middle – semi-neutral, lower – fully separated beams (Zharkova) 1.8 for p 2.2 for e 1.8 for p 2.2 for e 1.7 for p 4-5 for e 4-5 for p 2.0 for e 1.5 for p 1.8 for e