Electron Acceleration in the Solar Corona

1. Electron Accelerationin the Solar Corona Gottfried Mann Astrophysikalisches Institut Potsdam, D-14482 Potsdam e-mail: GMann@aip.de The Sun is an active star. flare  heating the coronal plasma  mass motions (jets, CMEs)  enhanced emission of electromagnetic radiation (radio, visible, X-ray, -ray)  energetic electrons  energetic protons energetic electrons  non-thermal radio and X-ray radiation

2. The RHESSI MissionThe Sun in the Hard X-Ray Light Ramaty High Energy Solar Spectroscopic Imager Reuven Ramaty (1937-2001) • NASA small explorer mission • PI – R.P. Lin (Space Science Laboratory, University of California, Berkeley) Launch: February 5, 2002 prolongation at least until September, 2008

3. The Instrument • fine grids modulate the X-ray radiation  15 rpm  30 images/minute by Fourier-transform technique • 9 cooled Ge crystals • energy resolution:  < 2 keV below 1 MeV  5 keV at 20 MeV • angular resolution:  2.3’’ for 3 – 100 keV  7’’ at 400 keV  36’’ above 1 MeV (1’’  730 km at the Sun) For the first time, RHESSI provides high-resolution hard X-ray images of the Sun. primary scientific objectives:• impulsive energy release • particle acceleration •particle and energy transport Processes with energetic electrons are the subject of the work at the AIP.

4. First RHESSI Observations I Solar event on February 26, 2002 (by courtesy of ETH Zürich)

5. First RHESSI Observations II 13:51 – 13:57 – hard X-ray emission (3 – 60 keV) – type III bursts (electron beams) 13:57 – 14:05 – type II burst (coronal shock) – type III’s

6. Interpretation of Solar Radio Spectra? Radio wave emission  plasma emission  drift rate: heliospheric density model(Mann et al., A&A, 1999) height from center of the Sun in Mio. km frequency in MHz height frequency velocity drift rate dynamic radio spectrogram  height-time diagram

7. First RHESSI Observations II 13:51 – 13:57 – hard X-ray emission (3 – 60 keV) – type III bursts (electron beams) ( 50000 km/s) 13:57 – 14:05 – type II burst (coronal shock) ( 1000 km/s) – type III’s

8. The solar event on April 21, 2002

9. Mechanism of Electron Acceleration basic question – electron acceleration in the solar corona energetic electrons  non-thermal radio and X-ray radiation electron acceleration  magnetic reconnection (Holman, 1985; Benz, 1987; Litvinenko, 2000)  shock waves(Holman & Pesses,1983; Schlickeiser, 1984; Mann & Claßen, 1995; Mann et al., 2001)  stochastic acceleration via wave particle interaction(Melrose, 1994; Miller et al., 1997)  outflow from the reconnection site (termination shock) (Forbes, 1986; Somov & Kosugi, 1997; Tsuneta & Naito, 1998; Aurass, Vrsnak & Mann, 2002)

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. 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

12. Shock Drift Acceleration I • fast magnetosonic shock magnetic field compression  moving magnetic mirror  reflection and acceleration non-relativistic approach(Ball & Melrose, 2003; Mann & Klassen, 2005)  shock normal:  magnetic field:  initial state: • transformation in the shock rest frame • transformation in the de Hoffmann-Teller frame

13. Shock Drift Acceleration II reflection in the de Hoffmann-Teller frame  conservation of energy  conservation of magnetic moment initial state: reflection condition: reflection: iv) transformation back to the laboratory frame

14. Shock Drift Acceleration III resulting distribution function:  shifted loss-cone distribution(Leroy & Mangeney, 1984; Wu, 1984)

15. Shock Drift Acceleration IV reduced distribution function: pure beam-like distribution  differential flux  electron number density of accelerated electrons  energy of accelerated electrons

16. Discussion I basic plasma parameters: termination shock:

17. Discussion II 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)

18. Electron Acceleration at the Solar Flare Reconnection Outflow Shocks Huge solar event on October 28, 2003 produced highly relativistic electrons seen in the hard X- and -ray radiation.

19. Outflow Shock Signatures During the Impulsive Phase Solar Event of October 28, 2003: RHESSI & INTEGRAL data (Gros et al. 2004)  termination shock radio signatures start at the time of impulsive HXR rise  outflow from the reconnection site (termination shock) (Forbes, 1986; Tsuneta & Naito, 1998; Aurass, Vrsnak & Mann, 2002 Aurass & Mann, 2004) The event produced electrons up to 10 MeV.

20. Further Observations Solar Event of October 28, 2003: • distance hard X-ray foot point sources 87 Mm • distance from the hard X-ray sources to the TS 350 Mm • sources area of the TS 2.9 • 104 (Mm)2

21. Relativistic Shock Drift Acceleration I • Lorentz-transformations: laboratory frame  shock rest frame  HT frame  back relativistic approach(Mann et al., 2006) using the addition theorem of relativistic velocities (Landau & Lifshitz, 1982) • motional electric field has been removed  conservation of kinetic energy: conservation of magnetic moment:

22. Relativistic Shock Drift Acceleration II  transformation of the particle velocities  reflection conditions:

23. Discussion III 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

24. Discussion IV electron distribution function in the corona – Kappa-distribution kinetic definition of the temperature phase space density (Maksimovic et al., 1997; Pierrard et al., 1999)

25. Discussion V 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 (Mann, Aurass & Warmuth, 2006).

26. Conclusions •  The termination shock is able to efficiently generate energetic electrons • up to 10 MeV. •  quantitative confirmations of Tsuneta & Naito‘s (1998) suggestion  Electrons accelerated at the termination shock could be the source of • nonthermal hard X- and -ray radiation in chromospheric footpoints • as well as incoronal loop topsources. • The same mechanism also allows to produceenergetic protons (< 16 GeV).

27. Summary The collection of space born data (RHESSI, SOHO, WIND, TRACE) and ground based observations (Tremsdorf Observatory, Observatorium Kanzelhöhe, Nancay Radio Heliograph) represents a virtual solar observatory and allows together with theoretical studies to get a deeper inside in the physical processes at the Sun.