Joint session WG4/5

Points for discussion:

- Soft-hard-soft spectral behaviour – again

- Non-thermal pre-impulsive coronal sources

- Very dense coronal loops (~ 1011 cm-3) and other dense structures

- Coronal sources that decrease in altitude (sometimes as footpoints approach), then increase

- tiny inferred size of flare footpoints high beam flux and implications

30-50 keV intensity

30-50 keV / 20-30 keV intensity ratio

50-70 keV / 30-50 keV intensity ratio

Correlation between impulsive phase intensity and spectral hardness - ubiquitous

Spectral soft – hard - soft

GOES 1-8 ADERIVATIVE

Non-thermal preflare coronal sources

RHESSI Preflare Maps 3-12 keV (color): 12-25 keV (contours)

01:07:00-01:08:30

01:08:00-01:10:30

01:11:00-01:12:30

Coronal source

RHESSI SPECTRA 5-50 keV Thermal+broken powerlaw Preflare period: 01:02:00-01:11:00

Broken powerlaw extends down to 5 keV Thermal component

never dominates EM and T are poorly

determined Chisquare ~ 1 if EM=0

White = photons, Green = thermal model,Red = broken powerlaw, Purple = background

(NB similar source in July 23rd 2002 event)

Dense coronal sources

Substantial high energy emission in corona: thermal and radio observations allow estimate of density – 1011cm-3

20-30 keV 30-50 keV 50-100 keV

20 July 2002, pixon image reconstruction

Descending loop top sources

Time evolution: blue white

Footpoints: 70-100 keVLoop top: 20-25 keV

H footpoint separation

HXR source ‘height’

Descending loop top sources – with decreasing footpoint separation

Flare footpoints – white light observations

WL coincides with HXR source locations – sizes at resolution of TRACE (few px = few 1000 km area ~ 1017 cm2)

M2.2 flare

Predicted ‘evaporation’ velocity as function of beam flux

Using A= 1018 cm2 Using A= 1017 cm2