Radio Studies of Solar Flares

The 1999 August 20 flare

• A strong limb flare (GOES class M9.8)

• High time cadence for the Max Millennium campaign

• The microwaves decay exponentially

• The hard X-ray emissions in the short impulsive phase

Lightcurves of microwaves and HXRs

Let me go on this event in some detail and the other ones I’ll go through more quickly. It was a strong limb flare, and observed as a part of the Max Millennium campaign. The OVSA was run at a high time cadence mode, 1 s resolution, instead at a reduced number of frequencies. The red/orange colors are microwave fluxes as a function of time & the white one is HXR from BATSE. What interested me most was the simple exponential decay curves similar at all frequencies. Note that flux is in log-scale while the time-axis is linear. Looked like a sort of uniformly varying decay time with frequency, which could be uniform variation in electron energy distribution. The HXR in this event was short-lived, which could mean that the injection was short this much (otherwise why HXR is short). Microwaves are OK to be longer if they are trapped in the corona as usual. So the usual injection and trap model would be appropriate, and looking for the morphology.