NONTHERMAL RADIO-EMISSION FROM SOLAR SOFT-X-RAY TRANSIENT BRIGHTENINGS

We compare microwave total power spectral data from the Owens Valley R adio Observatory Solar Array with soft X-ray transient brightenings ob served with the Yohkoh soft X-ray telescope. We find that the transien t brightenings are clearly detected in microwaves in 12 of 34 events ( 35%), possibly detected in another 17 of 34 events (50%), and only fiv e of 34 events (15%) had no apparent microwave counterpart. Comparing the radio and soft X-ray characteristics, we find that (1) the soft X- ray peak is delayed relative to the microwave peak in 16 of 20 events, (2) the microwave flux is correlated with the flux seen in soft X-ray s, (3) when radio fluence is used instead of radio flux (24 events) th e correlation increases substantially, (4) the microwave spectra in th e range 1-18 GHz vary greatly from event to event, (5) the microwave s pectra often peak in the range 5-10 GHz (13 of 16 events), and (6) the microwave spectra of some events show narrowband spectra with a steep low-frequency slope. We conclude that the emission from at least some events is the result of a nonthermal population of electrons, and tha t transient brightenings as a whole can therefore be identified as mic roflares, the low-energy extension of the general flare energy distrib ution. Soft X-ray transient brightenings, and therefore microflares, c annot heat the corona.