Institute of Astronomy, Radio Astronomy and Plasma Physics Group Eidgenössische Technische Hochschule Zürich Swiss Federal Institute of Technology, Zürich Flare Electron Acceleration Arnold Benz

1. RHESSI Observations Spectral evolution of flares

thermal non-thermal RHESSI two component fits: T, EM γ, F 35

Grigis & B. flux spectral index

P. Grigis

Battaglia et al. 2005

Δ●Δ● < C2 > C2 Δ Δ ● Battaglia & B., 2005

F HXR ─ γ Relation 1."Pivot" point at about 9 ± 3 keV (soft-hard- soft) 2.Consistent with constant acceleration rate above threshold energy (13.9 keV) 3.Consistent with constant total power in particles above threshold energy (13.6 keV) 4.Consistent with stochastic acceleration beyond 18.1 keV 5.Inconsistent with pure "statistical flare" scenario

Approximation for d << d c : f(E)  f o E -   f o  (WL) 7/8 anti-   (WL) -1/2 correlation !  E 1/2    f(E)  f(E)  t +  z  E  E E 1/2 +  t ( D E coll Diffusion by stochastic wave turbulence ( ( ( ( f(E) = Assume steady state => Bessel equation Solution: f(E) = C E - d + 1/2 K d (E) 1/L aW } Benz 1977 (

Approximate further, eliminate WL and get for observed HXR flux: F HXR  C (1/2 + 1/2[1 +  (  +3/2)] 1/2 ) 2 [(  - 1)(  +3/2) ] 2 log F HXR  Brown & Loran, 1985

2. RHESSI –Phoenix Observations

Type III Pulsations Narrowband spikes Diffuse cont. Type IV Type I Hf broadband (gyro-synchrotron) before rise peak decay after radio emission in 201 X-ray flares >C5.0

Meter-Decimeter Radio Patterns of X-ray selected flares A Standard 129 B Just III m 8 C Afterglows 20 D No Radio 34 E Type I 10

Standard

M1.1 Standard 25 – 50 keV 50 – 100 keV irreg. pulsation

Standard reversed drift III m 25 – 50 keV 50 – 100 keV M1.1

Standard irregular pulsation decimetric narrowband spikes 50 – 100 keV 25 – 50 keV M1.1

C7.7 Standard III dm irreg.pulsation hf continuum 6 – 12 keV 12 – 25 keV 25 – 50 keV

Just III m

C7.9 Just III m 6 – 12 keV 12 – 25 keV 25 – 50 keV

Just III m 6 – 12 keV 12 – 25 keV 25 – 50 keV C7.9

Type IV and DCIM "Afterglows"

type IV gyro- synchrotron Phoenix-2 Radio spectrum GOES Class X17 gyro- synchrotron drifting structure decimetric pulsations

Phoenix-2 Radio spectrum decimetric pulsations decimetric patch

Type IV DCIM

M – 25 keV 6 – 12 keV 3 – 6 keV Afterglows narrowband spikes III m and hf continuum

Afterglows 3 – 6 keV 6 – 12 keV 12 – 25 keV M2.3 regular dm pulsation patch

100 – 300 keV regular dm pulsations Afterglows 6 – 12 keV 12 – 25 keV 25 – 50 keV 50 – 100 keV M5.0

No Radio

radio-quiet flare GOES class M1.0 6 – 12 keV 12 – 25 keV 25 – 50 keV 50 – 100 keV

no-radio flares Flares C5.0 – C % Flares > M % All flares > C % Two possible interpretations: 1. Small flares have less radio emission (sensitivity effect) 2. Large flare have more associated processes ("large flare syndrom", suggesting indirect connection)

2 1 A B C Standard: reconnection at 1 and 2 Just III m : reconnection at 2 Type IV: reconnection at 2 after 1 Noise storm: reconnection at 2 Radio-quiet:: reconnection at 1

2 1 A Standard: reconnection at 1 and 2 Just III m : reconnection at 2 Type IV: reconnection at 2 after 1 Noise storm: reconnection at 2 Radio-quiet:: reconnection at 1

Summary on HXR - Radio Correlations Hard X-ray and radio emissions of flares are relatively independent. 17% of >C5.0 flares have no coherent radio emissions (22% if type I excluded). Many type III m have no hard X-ray emission. Correlation is often poor, suggesting multiple acceleration sites for "standard flare pattern" and "afterglows". Multiple reconnection may also interprete "big flare syndrom".

Conclusions 1.Where are electrons accelerated? - often in more than one site (independent signatures) - most III m (and SEDs) have only very weak hard X-ray emission (possibly high-coronal flares). 2. How are they accelerated? - Violent acceleration processes are excluded. - If acceleration signature, why not close X-ray correlation? - Radio type IV and DCIM indicate processes long after flare 3. If loop-top, why this large number? - loop-top may be secondary acceleration site

Observational Constraints on Flare Particle Acceleration 1.Absence of radio emission in 17% of flares does not support violent acceleration processes, such as single shocks or single DC fields. 2.Consistent with heating processes (bulk energization). 3.RHESSI observations show that flares start with soft non-thermal spectrum. In the beginning it is difficult to distinguish from a thermal spectrum (γ ≈ 8). 4. The spectrum of non-thermal electrons gets harder with flux of non- thermal electrons both in time during one flare, as well as with peak flare flux (Battaglia et al. 2005). 5. The evidence supports stochastic bulk energization to hot thermal distribution and, if driven enough with power-law wings.

III m irregular dm pulsation narrowband spikes reversed drift III dm Standard 6 – 12 keV 12 – 25 keV keV C9.0

6 – 12 keV II III dm HF cont. Standard 12 – 25 keV 25 – 50 keV X1.6 III dm

OVSA Standard Irregular pulsation C9.7

Standard 6 – 12 keV 12 – 25 keV C6.5 irreg.pulsation

Christe & Krucker Standard RHESSI

Just III m 6 – 12 keV 12 – 25 keV C8.0

Type I 12 – 25 keV 6 – 12 keV C7.3

Type I