YOHKOH/HXT Evidence for a Hyperhot Loop-Top Source in The Pre-Impulsive Phase of a Loop Flare

摘要: A loop flare that occurred on 22 April 1993 near the disk center is examined using Yohkoh Hard X-ray Telescope (HXT). We specifically looked into faint early phase of prior to start strong impulsive phase. The pre-impulsive phase, though weak in intensity, expected contain essential clues mechanism flares according causality principle, but it has not received attention previously, probably due insufficient dynamic range and cadence observations by instruments earlier satellites. Observations with Yohkoh/HXT can clarify what occurs this This flare, like many other type, shows a relatively emission smooth gradual increase during followed bursts, then turns decay without bursts. First, we found spectrum for initial rise part consistent thin-thermal source at temperature around 80 MK. Imaging HXT/L M bands single between footpoint sources will come up following suggesting hyperhot located high footpoints, since takes form loop. Furthermore, as go earliest times before `hyperhot' two fainter are appear later spectra these time contrast source, cannot be determined from HXT because instrument was mode, HXT/M1, M2, H-band data are, unfortunately, available very time. guess, however, they also thermal character profile any spikes just post-impulsive `superhot' coming much later. These findings suggest there an important, dynamic, been unnoticed still dark change top matter 20–30 s, comparable Alfven scale. Some implications our new discussed.