Title: Electron Acceleration at the Solar Flare Reconnection Outflow Shocks
1Electron 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
2Electron 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
3Outflow 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.
4Relativistic 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)
5Relativistic Shock Drift Acceleration II
? transformation of the particle velocities
? reflection conditions
6Discussion 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
7Discussion II
electron distribution function in the corona
Kappa-distribution
kinetic definition of the temperature
8Discussion 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.
9Summary
- ? 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).
10Radio 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
11Plasma 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
12Characteristics 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
13Discussion 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)