Fe XIX observations of active region brightenings in the corona

Abstract

Small flarelike brightenings seen in the hot flare line, Fe XIX, by the spectrometer SUMER on SOHO are analysed. We observe active region coronae about 30 Mm off the limb of the Sun for a period of several days. Brightenings are observed with a frequency 3-14 per hour and their lifetimes range from 5-150 min, with an average of about 25 min. The measured size of the events along the spectrometer slit range from 2-67 Mm, but most are around 7 Mm. Like soft X-ray active region transient brightenings, they range in estimated thermal energy from 10 26 to 10 29 erg with a power law index of 1.7 to 1.8, beyond 10 27 erg. We conclude that they are the coronal parts of loops heated to >6 MK by soft X-ray microflares.