High-Energy Electrons in Double-Loop Flares

We studied the fast temporal variations in the brightness of the radio and hard X-ray sources of three double-loop flares observed with the Nobeyama Radioheliograph, Yohkoh, and CGRO/BATSE. As shown in the figure (a) below, in such flares, the main radio/hard X-ray source is located near to one of the footpoints of a large overlying loop, where a small, newly emerging loop appears and the two loops interact, and the remote source is located at another footpoint of the large loop. Figure (b) schematically shows the configuration of the emerging loop and the overlying loop. The following results were obtained from the analysis:

(Hanaoka, Publ. Astron. Soc. Japan, 51, 483, 1999.)
(a) Soft X-ray image of a double-loop flare on 7 June 1993 overlaid by white contours showing the 17 GHz radio image and black contours showing the hard X-ray image. (b) Schematic drawing of the flare loops. (c) Changes in the hard X-ray and microwave intensities of the 7 June 1993 flare. (d) Relation between the assumed delay and the correlation coefficient between two of the rapidly fluctuating components shown in (c). The thick lines show the correlation coefficients between the time variation of the remote source and that of the main source, and the thin lines show the correlation coefficients between the time variation of the main source and another time variation of the main source.

(1) The main source and the remote source basically show a correlated brightness fluctuation in radio and hard X-rays, but the rapid fluctuation of the brightness of the remote source lags behind that of the main source for about 500 ms. This result is evidence that the electron-acceleration region is close to the main source and, therefore, it is most presumable that the high-energy electrons in the double-loop flares are accelerated in the interaction region of the two loops.

(2) The brightness of the hard X-rays from the main source and that of the microwaves from the remote source fluctuate highly, but the microwaves from the main source fluctuate less. This result means that the microwave-emitting electrons are effectively trapped at the main source region.

(Hanaoka, Publ. Astron. Soc. Japan, 51, 483, 1999.)