THE RADIO PROPERTIES OF SOLAR ACTIVE-REGION SOFT-X-RAY TRANSIENT BRIGHTENINGS

We present the results of a search for radio emission from active-region transient brightenings identified in Yohkoh soft X-ray telescope observations of active region AR 7260. We present detailed observations of four events in which 17 GHz radio emission is clearly detected in observations by the Nobeyama radioheliograph. The time profiles of the 17 GHz data are very similar to those of the soft X-ray fluxes, and the 17 GHz flux is very dose to that expected from plasma with the temperature and emission measure derived for the soft X-ray-emitting material from filter ratios. No impulsive nonthermal radio emission was detected from any of the four events, although each was at least GOES class B1 in soft X-rays. Weak hard X-rays may have been detected by GRO/BATSE from the strongest of the events, but not from two others. These negative results leave open the possibility that there is a difference between active region transient brightenings and solar flares, in that the former do not convert a significant amount of the released energy into accelerated electrons. However, confirmation of this hypothesis will require a larger sample of events.