Coordinated OVRO, BATSE, Yohkoh, and BBSO observations of the 1992 June 25 M1.4 flare

We compare 1-14 GHz microwave images observed at the Owens Valley Radio Observatory (OVRO), 16-and 256-channel hard X-ray spectra obtained by the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO), soft and and hard X-ray images obtained by Yohkoh, and Hα images and magnetograms observed at the Big Bear Solar Observatory (BBSO) for the 1992 June 25 M1.4 flare. We find the following unique properties for this flare: (1) Soft X-ray emissions connect two footpoints, the primary microwave source is located at one footpoint, and hard X-ray emissions are concentrated in the other footpoint. The radio footpoint is associated with an umbra and may have stronger magnetic field. (2) During the period that 256-channel BATSE data are available, the hard X-ray photon spectrum consists of two components: a superhot component with a temperature of 8.4 × 10⁷ K and emission measure of 2.5 x 10⁴⁶ cm^-3 and a power-law component with a photon index of 4.2. This is the first time that such a high temperature is reported for the hard X-ray thermal components. It is even more interesting that such a superhot component is identified before the peak of the flare. The microwave brightness temperature spectra during the same period also demonstrate two components: a thermal component near the loop top and a nonthermal component at the footpoint of the loop. The microwave thermal component has the similar temperature as that of the hard X-ray superhot component. These measurements are consistent with the theory that the microwaves and hard X-rays are due to the same group of electrons, despite the fact that they are separated by 35,000 km. (3) The soft X-ray emissions brighten the existing loops and co-align with Hα emissions throughout the entire duration of the flare.