Electron Acceleration at the Solar Flare Reconnection Outflow Shocks Gottfried Mann, Henry Aurass, and Alexander Warmuth Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D Potsdam, Germany 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)

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

basic coronal parameters at 150 MHz (  160 Mm for 2 x Newkirk (1961)) (Dulk & McLean, 1978) (flare plasma) shock parameter Discussion I total electron flux through the shock

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

relativistic electron production by shock drift acceleration The density of 8.54 MeV electrons is enhanced by a factor of 1.5  10 6 with respect to the undisturbed level in the phase space. Discussion III 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  drift rate: dynamic radio spectrogram  height-time diagram 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 ( 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