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Electron Acceleration at the Solar Flare Reconnection Outflow Shocks

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Title: Electron Acceleration at the Solar Flare Reconnection Outflow Shocks


1
Electron Acceleration at the Solar Flare
Reconnection Outflow Shocks
Gottfried Mann, Henry Aurass, and Alexander
Warmuth Astrophysikalisches Institut Potsdam, An
der Sternwarte 16, D-14482 Potsdam,
Germany e-mail GMann_at_aip.de
Huge solar event on October 28, 2003 produced
highly relativistic electrons seen in the hard
X- and ?-ray radiation by INTEGRAL
2
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
3
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.

4
Relativistic Shock Drift Acceleration I
  • fast magnetosonic shock ? magnetic field
    compression
  • ? moving magnetic mirror
  • ? reflection and acceleration
  • reflection in the de Hoffmann-Teller frame (see
    e.g. Ball Melrose, 2003 (non-rel. appr.))
  • Lorentz-transformations laboratory frame ?
    shock rest frame ? HT frame ? back
  • motional electric field has been removed
  • ? conservation of kinetic energy
  • conservation of magnetic moment
  • electrostatic cross-shock potential
    (Goodrich Scudder, 1984 Kunic et al., 2002)

5
Relativistic Shock Drift Acceleration II

? transformation of the particle velocities
? reflection conditions
6
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

7
Discussion II
electron distribution function in the corona
Kappa-distribution
kinetic definition of the temperature

8
Discussion III
relativistic electron production by shock drift
acceleration
phase space densities
The density of 8.54 MeV electrons is enhanced by
a factor of 1.5 ?106 with respect to the
undisturbed level in the phase space.

9
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).

10
Radio Observations of Coronal Shock Waves
  • type II bursts ? signatures of shocks
    in the solar radio radiation
  • (Wild McCready, 1950 Uchida, 1960 Klein et
    al., 2003)
  • two components
  • backbone (slowly drifting ? ? 0.1
    MHz/s)
  • ? shock wave
  • (Nelson Melrose, 1985
  • Benz Thejappa,
    1988)
  • ? herringbones (rapidly drifting ? ? 10
    MHz/s)
  • ? shock accelerated
  • electron beams
  • (Cairns Robinson, 1987
  • Zlobec et al., 1993
    type II burst during the
    event
  • Mann Klassen, 2002)
    on June 30, 1995

11
Plasma Emission Interpretation of Solar Radio
Spectra
radio wave emission ? plasma emission
? drift rate
heliospheric density model (Mann et al., AA,
1999)
frequency in MHz
height from center of the Sun in Mio. km
height frequency velocity
drift rate
dynamic radio spectrogram ? height-time diagram
12
Characteristics of Termination Shock Signatures
  • no or very slow drift
  • at comparatively
  • high frequencies
  • (320-420 MHz)
  • split band structure
  • herringbones
  • characteristics closely resemble ordinary
    type II bursts ? shock
  • but no drift, stationary in radioheliogams
    ? standing shock
  • located above flaring region
    ? termination
    shock

13
Discussion III
comparison with usual type II bursts ?
Coronal shock waves (type II bursts) are usually
not able to produce a large number of
energetic electrons than during at a flare (Klein
et al., 2003). ? Usual type II bursts appear
below 100 MHz (fundamental radiation). ?
Type IIs related with the termination shock
appear around 300 MHz ? Comparing electron
fluxes in the upstream region quiet
corona at 70 MHz and 1.4 MK flaring
plasma at 300 MHz and 10 MK (maximum
temp. 38 MK)
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