WG7 Particle acceleration and transport

							WG7: Particle acceleration
     and transport
            Regular Participants
D. Alexander       M. McConnell
M. Aschwanden      M. Piana
T. Bastian         A. Shih
J. Brown           R. Turkmani
S. Christie        N. Vilmer
E. Chupp           L. Vlahos
C. Dauphin         A. Warmuth
M. Gordovsky       S. White
J. Gosling         T. Winter
G. Hurford         V. Zharkova
A.M. Massone       And many visitors and invited
                    speakers (R. Lin, G. Share, E.
                        Kontar)
                             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.
      Characteristics of Particle
       accelerator in the sun
 Theme 1: The energy distribution of the
  accelerated particles fe,i ( E ) 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
Mean Electron Spectrum: Temporal evolution
(Kontar)
               1234 5                    RHESSI Lightcurves
                                         3-12keV;
                                         12-25keV;
                                         25-50keV;
                                         50-300keV


Temporal evolution of the                   3
Regularized Mean Electron
Spectrum (20s time intervals)


                                12 4 5
Accelerated (injected) Electron Spectrum(Kontar)
  Accelerated (injected) electron spectrum for a thick-target model:




Temporal evolution of the
Regularized Accelerated                              3
Electron Spectrum
(20s time intervals)


                                       12 4 5
     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
Solar energetic particles at 1AU (Krucker-Kontar)
Evidence for Electron Spectral Hardening (Share)
        Characteristics of Particle
         accelerator in the sun
   Theme 2: Very high energy particle
    (Vilmer)
        -ray and neutron event on 24/05/90 (Vilmer)
                           High Energy -rays    From Talon et al., 1993
                                                 Debrunner et al 1997
                           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
                                           Background subtracted count spectra
                                           From PHEBUS/GRANAT
                                           Full line: one of the best fits with
                                           electron and pion contributions
                                           Dotted line: electron contribution




Background subtracted count spectrum                           -ray lines
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
        Characteristics of Particle
         accelerator in the sun
   Theme 3: Anisotropies
                  f ( E,  )

   (Alexander, McConnell, Bastian)
      Asymmetric footpoints (Alexander)

I1

         F1
                  F2




Following AM02 we define the footpoint photon asymmetry as


                             I 2  I1
                       A
                             I 2  I1


where Ii denotes the count rate at footpoint i. For perfect symmetry
A = 0 and for perfect asymmetry A = ±1.
         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)
          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

                  1037 particles / sec
   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)
      Characteristics of Particle
       accelerator in the sun
 Theme 5: Magnetic topology (S. White,
  Alexander) and its role on acceleration
  and transport…
 Complexity vs simplicity
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)
 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)
          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)
                                                        50- 180 keV

Time delays in -ray line
emission can be as small                                  275- 325 keV
as <2 sec to as large as
10’s of sec.
-ray line emission in                                    4 – 6.4 MeV

2002 July 23 flare may
be delayed by ~10 sec                       |-----20 sec----|

from hard X-rays.
What does this say
                                                        50- 180 keV

about acceleration-
transport? Could be                                       275- 325 keV
accounted for by
trapping or is it intrinsic
to the acceleration           4 – 6.4 MeV
process? (Share)

                                            |------100 sec------|
      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?
      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
          Core
 =>
solar wind plasma
 electrons                  Solar Wind
                             Electrons

     Halo/Strahl
 => heat flux from ~106 K
 corona


 Superhalo
 =>
remnant from coronal
 heating or solar wind
 acceleration?
     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
          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
                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)
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.
Macroscopic description (MHD) (Galsgaard)
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
Electric field
                 E = -(u x B) +  J

                     Inductive   Resistive
Time evolution and
Distribution functions (Turkmani)
Accepted current sheet scheme
                 (Zaharkova)
Energy spectra:        e (blue) and p (black)
upper panel – neutral, middle – semi-neutral,
lower – fully separated beams (Zharkova)

                    1.8 for p                     1.8 for p
                    2.2 for e                     2.2 for e



                       1.7 for p                4-5 for p
                       4-5 for e                2.0 for e


                        1.5 for p               1.8 for e