The hard X-ray spectral structure of flare ribbons

H. Hudson, L. Fletcher,

S. Krucker, J. Pollock

Yohkoh Bastille Day Flare 2000(Masuda et al. 2001)

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RHESSI April 21, 2002(B. Dennis)

Hard X-rays show traces of the ribbons

Model and Problems

• Model: The ribbon (footpoint) emissions from precipitating electrons (Kane & Donnelly, 1971)

• Problem: The UV ribbons consist of multiple simultaneous kernels, not simple footpoints

• Problem: There are other clear morphological differences (Warren & Warshall 1999)

29-October 2003 RHESSI illustration

Greater complexity: 17 July 2002 event(Fletcher et al., Solar Physics 222, 279, 2004)

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Fletcher et al.

Klimchuk McKenzie

Multiple reconnection points might leadto multiple footpoints, but…

• There is no model for the complex separatrix structure expected then(cf. Linton-Longcope SH13A-1160).

• Why do some reconnection events produce hard X-rays and others only UV?

Two scenarios

• Ribbon structure may form independently of any electron beams.

• The electron beams carry the energy, all right, but have softer spectra outside the hard X-ray footpoints.

Mariska, Emslie, & Li, ApJ 341, 1067 (1989)

In R-H numerical models, softer electron spectra produce stronger chromospheric evaporation

120 sec

June 17, 2002 UV/HXRcomparisons

Trace 1600 A

Trace WL

The July 17 flare shows the expected correlations, but no obvious HXR spectral structure

Conclusions & Speculations

• We have no real results yet from the UV/HXR correlations

• Still expect to use RHESSI imaging spectroscopy to see the predicted spatial effects

• Speculate that WL/IR ribbon structure may guide us to electron beam energy (cf. Xu et al., ApJ 2004)

• Speculate that there may be signatures of 3D magnetic structure in the UV/HXR differences