Group V: Report

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Group V Report

• Regular Members K. Arzner, A. Benz, C. Dauphin,
  G. Emslie, M. Onofri, N. Vilmer, L. Vlahos
• Visitors E. Kontar, G. Mann, R. Lin, V. Zharkova

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Main Goals

• Constrains on particle acceleration from the
  RHESSI data (close collaboration with all WGs)
  and other available sources of information on
  high energy particles
• Discuss new theories on particle acceleration
• Connecting theories on particle acceleration with
  the global magnetic topologies hosting flares and
  CMEs

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Constraints on Acceleration/Transport(Electrons)

• Must produce an electron flux of at least 1037
  electrons per second
• Must be able to accelerate electrons on time
  scales at most 10 milliseconds
• Must sometimes produce electron energies greater
  than at least 10s of GeV
• Mechanism must be able to produce a flattening of
  the electron distribution at energies on the
  order of 500 keV
• Higher nonthermal hard X-ray flux statistically
  associated with harder spectra

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The Electron Problem

• Efficiency of bremsstrahlung production 10-5
  (ergs of X-rays per erg of electrons)
• ?Electron flux 105 ? hard X-ray flux
• Electron energy can be 1032 1033 ergs in large
  events
• Total number of accelerated electrons up to 1040
  (cf. number of electrons in loop 1038).
• replenishment and current closure necessary

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Revised Numbers
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X/?? -ray spectrum
Thermal components
T 2 10 7 K T 4 10 7 K
Electron bremsstrahlung
Ultrarelativistic Electron Bremsstrahlung
?-ray lines (ions gt 3 MeV/nuc)
SMM/GRS Phebus/Granat Observations GAMMA1 GRO GONG
Pion decay radiation (ions gt 100
MeV/nuc) sometimes with neutrons
RHESSI Energy range
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Electron-Dominated Events

• First observed with SMM (Rieger et al, 1993)
• Short duration (s to 10 s)
• high energy (gt 10 MeV) bremsstrahlung emission
• No detectable GRL flux
• Photon spectrum gt 1 MeV (?X?-1.52.0)
• For 2 PHEBUS events
• if Wigt1MeV/nuc ? Wegt20 keV
• No detectable GRL above continuum
• Weak GRL flares?

Vilmer et al (1999)
BATSE
PHEBUS
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non-thermal
thermal
RHESSI two component fits T, EM ?, F35
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spectral index
flux
Grigis B.
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Energy dependent photon spectral index
Interval 3 (peak of the flare)
Spectral index evolution
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Mean Electron Spectrum Temporal evolution
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3
5
RHESSI Lightcurves 3-12keV 12-25keV 25-50keV 50
-300keV
2
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Temporal evolution of the Regularized Mean
Electron Spectrum (20s time intervals)
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1
2
5
4
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Non-thermal preflare coronal sources
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RHESSI SPECTRA 5-50 keV Thermalbroken
powerlaw Preflare period 010200-011100

• Broken powerlaw extends down to 5 keV
• Thermal component never dominates
• EM and T are poorly determined
• Chisquare 1 if EM0

(NB similar source in July 23rd 2002 event)
White photons, Green thermal model, Red
broken powerlaw, Purple background
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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
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Ions

• Tens of MeV ions and hundreds of MeV particles
  can be accelerated at the same time
• We also see cases where we see a stage when
  hundreds of MeV ions are primarily accelerated.

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g-ray line emission can be delayed from hard
X-rays from lt2 to 10s of sec.
50- 180 keV
275- 325 keV
4 6.4 MeV
-----20 sec----
50- 180 keV
275- 325 keV
4 6.4 MeV
------100 sec------
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June 3, 1982 - Evidence for delayed high-energy
emission
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Constraints for Theory

• Radio spectral features and flares
• Connection between hard X-ray features and spikes
  in the range 300-3000 MHz, corresponding to
  densities of 109 -1011, has always been a
  promising diagnostic of energy release
• But there are some aspects hard to understand
  frequently the spikes occur in a narrow frequency
  range for 10s of seconds, implying a fixed
  density in the energy release site. Energy
  release widespread over a large volume would
  produce spikes over a wide frequency (i.e.
  density) range
• Wide range of burst types in this frequency range
  is hard to understand what controls frequency
  drift rates of different features?

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Radio Emission at Decimetric Wavelengths
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Constraints for Theory

• Magnetic configuration of flares in the low
  corona
• See configurations of all types in radio images
  single loops, double loops, complex
  configurations
• Frequently see magnetic connections over very
  large spatial scales
• Magnetic field strength spectra typically imply
  500-1000 G in the radio source
• But radio spectra are frequently flat-topped
  hard to model, range of fields in the source
  (need FASR)
• See both prompt precipitation, implying either
  rapid scattering of electron pitch angles or
  loops with little height dependence for B, and
  trapping, where radio is strong but X-rays are
  weak, implying little pitch angle scattering.

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Radio Flare Loop
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are the magnetic and kinetic Reynolds numbers.
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t (s)
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Energy spectra e (blue) and p (black)upper
panel neutral, middle semi-neutral, lower
fully separated beams
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
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The suggested scheme of proton/electron
acceleration and precipitation
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Electron Acceleration in Solar Flares
basic question particle acceleration in
the solar corona energetic electrons ?
non-thermal radio and X-ray radiation

• electron acceleration mechanisms
• ? direct electric field acceleration (DC
  acceleration)
• (Holman, 1985 Benz, 1987 Litvinenko,
  2000
• Zaitsev et al., 2000)
• ? stochastic acceleration via
• wave-particle interaction
• (Melrose, 1994 Miller et al., 1997)
• ? shock waves
• (Holman Pesses,1983 Schlickeiser, 1984
  
• Mann Claßen, 1995 Mann et al., 2001)
• ? outflow from the reconnection site
• (termination shock)
• (Forbes, 1986 Tsuneta
  Naito, 1998
• Aurass, Vrsnak Mann, 2002)

HXR looptop
HXR footpoints
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Outflow Shock Signatures During the Impulsive
Phase
Solar Event of October 28, 2003

• X17.2 flare
• RHESSI INTEGRAL data (Gros et al. 2004)
• termination shock radio signatures start
• at the time of impulsive HXR rise
• signatures end when impulsive
• HXR burst drops off

The event was able to produce electrons up to 10
MeV.

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Discussion I
basic coronal parameters at 150 MHz (? 160 Mm
for 2 x Newkirk (1961)) (Dulk McLean,
1978) (flare plasma)
shock parameter
total electron flux through the shock

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Summary

• ? The termination shock is able to efficiently
  generate energetic electrons
• up to 10 MeV.
• ? Electrons accelerated at the termination
  shock could be the source of
• nonthermal hard X- and ?-ray radiation in
  chromospheric footpoints
• as well as in coronal loop top sources.
• The same mechanism also allows to produce
  energetic protons (lt 16 GeV).

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Summary

• The constrains on the acceleration are becoming
  so many and the ability of a single acceleration
  to handle all this become impossible- No unique
  acceleration
• Shocks, stochastic E-Fields and turbulent
  acceleration enters into the picture
• Synchronized from photosheric motions complex
  magnetic topologies maybe be the answer