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@aip.de

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