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: [email protected]
Huge solar event on October 28, 2003
produced highly relativistic electrons
seen in the hard X- and -ray radiation
by INTEGRAL
Electron Acceleration in Solar Flares
basic question: particle acceleration in the solar corona
energetic electrons non-thermal radio and X-ray radiation
HXR footpoints
HXR looptop
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)
radio observations of termination shock signatures
Outflow Shock Signatures During the Impulsive Phase
• 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
Solar Event of October 28, 2003:
The event was able to produce electrons up to 10 MeV.
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)
const2HT,
2HT,II
constB
constB
p
HT
2HT,
HT
2HT,
)neglectedbecan(Tk8.31N
NTk
)1(e B
)1(
up
downBHT
transformation of the particle velocities
downuplc
II,is2s
Ic,i
sII,i
B/Bsinarc:angleconeloss
)(1
tan
Relativistic Shock Drift Acceleration II
};{}{ ,rII,r,i;II,i
c/secv
ß21
)1(
21
)1(2
n,Bss
,i2ssII,i
2s
,r
2ssII,i
2sII,is
II,r
reflection conditions: lc*s cos
basic coronal parameters at 150 MHz
( 160 Mm for 2 x Newkirk (1961))
(Dulk & McLean, 1978)
(flare plasma)
s/km610v
s/km300.12v
MK10T
G7.4B
cm108.2N
A
e,th
o
38e
2shock
s
Aupdownupdown
)Mm(64A
s/km1500v
32.2M2B/BN/N
shock parameter
Discussion I
total electron flux through the shock
134AAshockoe s105.2MvANP
Discussion II
electron distribution function in the corona – Kappa-distribution
2e
2/32
1
cm/Ewith
)2/1(
)1(
)c2(
1C
E
E1Cf
kinetic definition of the temperature
10andMK10Tforsin87.691)1(
)2(1009.7
sin)2/3(
1)1(
)2(cC2
dd
)(Nd
N
1
)2/3(cm
TkTkN2/3E
114
3
1
th43
o
2e
BhtB
relativistic electron production by shock drift acceleration
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.
28
o
34
o
1062.3dd
)MeV57.2(Nd
N
1
1036.2dd
)MeV54.8(Nd
N
1
Discussion III
MeV57.2E
027.5
74,6
1157.0
9793.0
i
i
i
,i
II,i
MeV54.8E
68.16
25,2
0393.0
9976.0
r
r
r
,r
II,r
993.0s
71.89n,B
phase space densities
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 (< 16 GeV).
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
height frequency
velocity drift rate
radio wave emission plasma emission
ee2 mNef drift rate:
dynamic radio spectrogram height-time diagram
sourcef Vdr
dN
N
1
2
f
dt
dfD
heliospheric density model (Mann et al., A&A, 1999)
frequency in MHz
height from center of the Sun in Mio. km
Plasma Emission & Interpretation of Solar Radio Spectra
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
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 II’s 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)
Discussion III
)keVscm/11015.5j(
4.18)MHz70(N
)MHz300(N
)s/km26400(keV2at106.8)MK4.1,MHz70(j
)MK10,MHz300(j
2210
0
0
4