Energetic Electrons in a Flaring LoopH. Nakajima, J. Sato, Y. Hanaoka, M. Shimojo,and A. Asai

Microwave & HXR observations of the 2002 Aug 24 flare on or behind the W-limb. Showed a clear loop like structure.Observations NoRH: the whole course of the duration. RHESSI: only the rising phase.

MotivationEHXR 100 keV, E34GHz 1 MeVStructural & spectral relationship bet. Microwave & HXR.Some information on acceleration of ele. & pitch angle distribution of accelerated ele..Explanation of Masuda flares.

A big and long-duration flare (GOES: X3.1, >3hrs)34GHz: always optically thin.Conducted analyses around 00:56 UT.First peak

TRACE Movie of ~106 plasma (19500:41 UT ~ 01:40 UTN-FT:Behind the limb.S-FT:Just on the limb.

Microwave Loop 34GHz: Spat.res. ~ 8x9Dist. Betwn FPs: 60Loop width: 14.40.5 Loop top source: visible.34 GHz contour level: 0.1, 0.25, 0.5, 0.75

Contour:0.1, 0.25, 0.5, 0.7534GHzimage

South FTNorth FPDistance (arcsec) along the loop axisTbBrightness distr.along the loopBothloop top source &footpoint sourceexist.(corresponds to trap & prec.components.)top

Loop topNorth FP (x1.7)South FPFirst PeakDecay time const.: ~ 30 sPeak delay: 4~10Time (s)Bs > Bn >Bt

= 2.4 = 4.0Ramaty code: B = 300 Gauss, = 80,source size = 25wavespectrum

B=300 Gauss Effective energy of ele. at 34 GHz is > 1 MeVBastian(1998)17 GHz

HXR images:

Color: 6 12 keVContour: 30 - 50keVLoop height: decreases with decreasing height.

Overlay of 17GHz& HXR imagesHXR image: 30 - 50 keV10% step from 10% Loop top source: 14x 24HXR loop top source:higher than 17 GHzSource by 7 5N-FT: no FT emiss.S-FP: --FT emiss. HXR -- no FT emiss.Asymmetrical loop!HXT: Spat. Res. ~ 10

HXR spectral fittingE > 10 keV:Double pow.law E < 34 keV = 5.7E > 34 keV = 7.0

Both the HXR image and thick-thin spectrum: consistent with trapping of ele. in the loop. Electrons ~34 should die in the corona. The transition energy of ele. Et ~ 34 keV (= HXR trans. energy) Et = { (N/1020)(0.7 /cos 1/2 20 keV N (column depth) = (21010)(3.9109) = 7.81019 cm-2 : average pitch angle distribution

cos = 0.19 = 79

Result34GHz flare:The flaring loop at 34 GHz had roughly uniform width (14.4 0.5), probably suggesting a small mirror ratio (M=Bfoot/Btop). This is consistent with small peak delay of Tb of the top with respect to those at the footpoints. Loss cone angle : sin2= 1/M = {(14.4-0.5) /(14.4)}2 ~ 75 M ~ 1.07Both a loop top component and footpoint components existed.Microwave spectrum:Elect. spectr. index = = 4.0 0.9, B ~ 300 Gauss

HXR flare at energy of 30-50 keV:Clearly a loop top source existed. Almost entire emission came from the coronal part. The HXR loop top source was located slightly above the microwave source with the same loop width. The microwave source was located at the same height as the lower energy source. HXR spectrum:Thick-thin HXR emission suggests a large pitch angle distribution (average 80) of electrons. consistent with Fretcher & Martens model for the Masuda FlareElectron spectrum index is estimated to be 6.0 ~ 6.7, which is significantly softer than spectrum index (4.0) from microwaves. need an additional acceleration for MeV electrons.

Pitch angle distribution of MeV electrons responsible for microwaves If we assume that electrons responsible for 34 GHz emission has a uniform pitch angle distribution. Tb N B3.4 (sin)2.2 N ( B ~ const., ~90) Nttrap/ Ntpre is estimated to be roughly 1/3 from obs.. On the other hands, Nttrap/ Ntpre is calculated to be {79 90 sin d / 0 79 sin d} = 0.35

MeV electrons may have roughly a uniform pitch angle distribution!

South FTNorth FPDistance (arcsec) along the loop axisTbBrightness distr.along the 34 GHz loop

Melnikov,Et.al,2002BFT /Btop=2