Stephen White on Radio/HXR Spectral Catastrophe - Joint with WG3

Summary (by LF): The electron energy spectral index calculated from 35-80 GHz radio emission, assuming optically-thin gyrosynchrotron emission, does not agree with that calculated assuming HXR emission by thick-target bremsstrahlung. However, we think that these are the same electron populations. The source of this mismatch should be investigated.

  • Radio data for July 23 event
    - NoRP fixed frequencies => high peak frequency
    - Is there RSTN or maybe other data?
    - footnote. The pre-flare non-thermal hard X-ray coronal source... has no counterpart at 35 GHz, at least on a linear plot. Need to look at a log plot!

  • Discussion: 35-80 GHz radio spectral index "wrong", explained in terms of optically-thin gyrosynchrotron emission: radio -2.5 or -3 energy index, as opposed to X-ray -4 or 4.5. If there were residual optical depth at 35 GHz; high harmonics give upper limit of 200 G for B. The only way to get such opacity would therefore be non-thermal particle density
    - Radio spectra: to get opacity at high frequencies, one really needs relativistic electrons. Recall McTiernan thesis regarding transition to relativistic cross-section
    - Silva, Wang, Gary paper with many examples of this problem; flux correlation looks normal (BFS-like). A bimodal distribution of spectral indices suggesting some agreements, but with others interpreted as broken power laws. Early paper by Benz and Gold recalled.
    - Standard bremsstrahlung ideas => alpha = -1.20 +0.90*delta for the radio flux spectral-index comparison, in isotropic distribution

  • Requirements:
    - Need source maps to match at the two high frequencies used for spectral determination. Comment (Hurford) about distributions of parameters (source inhomogeneity, filling factor).
    - Need to model radio spectra. Discussion of bounce time scales, beaming, how one compares the semi-trapped coronal population with the thick-target rate. "No trapping" (White) may allow trapping on bounce time scale, which could in princple affect the spectral distribution.
    - Need to compare absolute fluxes (Hurford comment) to learn about spectral modification during loss-cone replenishment. Suggestion of wave scattering with different spectral dependence from ordinary Coulomb or bremsstrahlung collisions (Hudson comment)
    - We need FASR!!
    Last modified: Tue Sep 23 13:05:14 BST 2003