Brightening event in Hα and soft X-ray on May 18, 1994 Original Research Article

By using Yohkoh soft X-ray images, vector magnetograms and Hα filtergrams, a brightening event that occurred on May 18, 1994 has been studied in detail. It occurred in a nearly potential large-scale magnetic configuration as shown by the comparisons between the magnetic extrapolations (linear force-free field) and the large-scale soft X-ray loops. This brightening event observed in Hα line and soft X-ray seems to be related to new emerging magnetic flux with an amount of photospheric magnetic flux of about 3 × 1020 Mx. The emerging flux increases obviously about 20 minutes before the Hα and soft X-ray brightening, and lasts for about 103 s. This brightening may be a signature of reconnection taking place between the pre-existing loop and the new emerging small loops.