Institute of Astronomy,Radio Astronomy and Plasma Physics GroupEidgenssische Technische Hochschule ZrichSwiss Federal Institute of Technology, ZrichFlare Electron Acceleration

Arnold Benz

1. RHESSI ObservationsSpectral evolution of flares

thermalnon-thermalRHESSItwo component fits:T, EM, F35

Grigis & B.fluxspectral index

P. Grigis

P. Grigis

Battaglia et al. 2005

< C2 > C2Battaglia & B., 2005

FHXR Relation"Pivot" point at about 9 3 keV (soft-hard-soft)Consistent with constant acceleration rate above threshold energy (13.9 keV)Consistent with constant total power in particles above threshold energy (13.6 keV)Consistent with stochastic acceleration beyond 18.1 keVInconsistent with pure "statistical flare" scenario

Approximation for d Bessel equationSolution: f(E) = C E -d + 1/2 Kd(E)1/LaW}Benz 1977(

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

2. RHESSI Phoenix Observations

Type IIIPulsationsNarrowband spikesDiffuse cont.Type IVType IHf broadband(gyro-synchrotron)beforerisepeakdecayafter radio emission in 201 X-ray flares >C5.0

Chart2

52315162

32739133

149

2212192

1423

151

2214017

213207

14116

18

2931

1421

11

42

5132

2

1

1

1

70

2

ViewAll

72318162

32840133

149

2212192

1423

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2234119

213208

15127

18

2931

3431

22

42

5142

2

11

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242034

11

173

2

ViewAlle

72318162

32840133

149

2212192

1423

151

2234119

213208

15127

18

2931

3431

22

42

5142

2

11

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11

242034

173

2

Sheet1

beforerisepeakdecayafter

Type III

regular metric72318162

decimetric32840133

broadband, m-dm149

reversed drift, dm2212192

slow drift, dm1423

Pulsations

quasi-periodic151

irregular2234119

drifting-up, irreg.213208

diffuse15127

Diffuse continuum

broadband18

drifting up ridge, II2931

patch3431

drifting down, patch22

Narrowband spikes

metric42

decimetric5142

Type IV assoc.2

Type IV

pulsations11

intermediate drift1

parallel dr. Bands

sudden reductions11

Type I242034

Hf broadband

hf broadband173

hf broadband only2

Sheet2

Sheet3

Meter-Decimeter Radio Patternsof X-ray selected flares

A Standard 129 B Just IIIm 8 C Afterglows 20 D No Radio 34 E Type I 10

Standard

M1.1Standard25 50 keV50 100 keVirreg.pulsation

Standardreverseddrift IIIm25 50 keV50 100 keVM1.1

Standardirregularpulsationdecimetricnarrowband spikes50 100 keV25 50 keVM1.1

C7.7StandardIIIdmirreg.pulsationhf continuum6 12 keV12 25 keV25 50 keV

Just IIIm

C7.9Just IIIm6 12 keV12 25 keV25 50 keV

Just IIIm6 12 keV12 25 keV25 50 keVC7.9

Type IV and DCIM "Afterglows"

type IVgyro-synchrotronPhoenix-2Radio spectrumGOESClassX17gyro-synchrotrondrifting structuredecimetric pulsations

Phoenix-2Radio spectrumdecimetric pulsationsdecimetric patch

Type IVDCIM

M2.312 25 keV6 12 keV3 6 keVAfterglowsnarrowband spikes IIIm andhf continuum

Afterglows3 6 keV6 12 keV12 25 keVM2.3regular dmpulsationpatch

100 300 keVregular dmpulsationsAfterglows6 12 keV12 25 keV25 50 keV50 100 keVM5.0

No Radio

radio-quiet flareGOES class M1.06 12 keV12 25 keV25 50 keV50 100 keV

no-radio flaresFlares C5.0 C9.9 22 %Flares > M1.0 12 % All flares > C5.0 17 %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)

21ABCStandard: reconnection at 1 and 2Just IIIm: reconnection at 2Type IV: reconnection at 2 after 1Noise storm: reconnection at 2Radio-quiet:: reconnection at 1

21AStandard: reconnection at 1 and 2Just IIIm: reconnection at 2Type IV: reconnection at 2 after 1Noise storm: reconnection at 2Radio-quiet:: reconnection at 1

Summary on HXR - Radio CorrelationsHard 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 IIIm 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".

ConclusionsWhere are electrons accelerated? - often in more than one site (independent signatures) - most IIIm (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 Absence of radio emission in 17% of flares does not support violent acceleration processes, such as single shocks or single DC fields.Consistent with heating processes (bulk energization).RHESSI observations show that flares start with soft non-thermal spectrum. In the beginning it is difficult to distinguish from a thermal spectrum ( 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.

IIImirregular dmpulsationnarrowbandspikesreversed driftIIIdmStandard6 12 keV12 25 keV25 - 50 keVC9.0

6 12 keVIIIIIdmHF cont.Standard12 25 keV25 50 keVX1.6IIIdmIIIdm

OVSAStandardIrregular pulsationC9.7

Standard6 12 keV12 25 keVC6.5irreg.pulsation

Christe & KruckerStandardRHESSI

Just IIIm6 12 keV12 25 keVC8.0

Type I12 25 keV6 12 keVC7.3

Type I