HIGH-ENERGY FLARE EXPLOSIONS DRIVEN BY 3-DIMENSIONAL X-TYPE CURRENT LOOP COALESCENCE

We present a model for high-energy solar flare explosions driven by 3-dimensional X-type current loop coalescence. The 3-dimensional X-type current loop coalescence, where two crossed flux-tubes interact at one point, is a fundamentally new process as compared to the 1-D and 2-D cases studied earlier. This process is studied by a first-order approach of the relevant variables near the point of coalescence; it appears to yield reliable information in a sufficiently large area around this point. It is shown that, following a strong plasma collapse due to the pinch effect, a point-like plasma explosion can be driven while fast magnetosonic shock waves can also be excited. We found that the conditions in the area producing the remarkable flare bursts of 21 May, 1984 were indeed such that the many flare spikes could have been due to 3-D explosive X-type current loop coalescence. We also show, by studying the conditions of shock formation in a gamma ray flare, that the time delay of gamma-rays from the impulsive phase could be the time needed for the shock formation in the flaring region. We draw some general conclusions on the question why certain flares do emit gamma-rays in the MeV energy range, and why other, apparently important and energetic flares, do not. We accentuate the fact that a well-developed high-energy flare has three phases of particle acceleration.