Ongoing Issues

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Contents

Number problem


Pre-flare


Spectral issues


Type III emission


Gamma-rays

How can such a plasma not be detectable by other means? (Hudson)


HXR footpoint issues

0. Number: Why are there usually two hard X-ray footpoints when there are many more points, and ribbon-like structure, at other wavelengths in the impulsive phase?

1. Timing: RHESSI should be able to do footpoint timing at the 0.1s level with visibilities (Hurford)

2. Flux ratios, spectral index differences: Double footpoint flares: do we have correlation between spectral index difference and flux ratios? --> Actually, some. Saint-Hilaire et al. (2008) have demonstrated that differences in column densities between leg of loops cannot explain all observed footpoint spectral index differences and flux ratios. Some other important mechanism is at play, most probably magnetic mirroring. Liu et al. (2008) basically agree, saying that neither a difference in column densities nor magnetic mirroring alone can explain all observations: we have interplay between the two (or there is even something else that comes into play).

3. Are spectral breaks the same for both footpoints?


Flare T, EM

Hottest temperatures in flares (45 MK) occur early in flare, at end of HXR emission (Neupert effect). EM goes on to rise and peaks much later (Caspi). In an event analysed by Saint-Hilaire et al. (2009), EM increases during more than 10 hours.


Chromospheric Evaporation

Is chromospheric evaporation the main source of all the hot plasma seen in the corona? EIS observations at different temperatures can address this question.

Neutral SEPs


Energetics

RHESSI has made an important contribution in terms of seeing the downward motions of early sources (Sui, Veronig, Ji).



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