A Microwave Study of Coronal and Chromospheric Ejecta

We have studied the radio properties of 18 X-ray coronaljets (observed by the Yohkoh SXT) using Nobeyama 17 GHz data. We also searched for chromospheric ejecta (Hα surges) during the time intervals that the X-ray images were available. Microwave emission was associated with the majority of the X-ray jets. The radio emission came from the base or the lower part of the jets. We detected radio emission from almost all jets which showed flare-like activity at their footpoints. The 17 GHz time profiles were gradual and unpolarized, implying that the emission was thermal. When possible, we computed the physical properties of the X-ray-emitting ejected plasma. In one two-sided-loop type jet and one anemone-type jet, the observed microwave fluxes from the lower part of the jets were well above the fluxes predicted from the computed electron temperatures and emission measures of the soft X-ray-emitting material on the basis of thermal free-free emission. We interpreted the large discrepancies in terms of the presence of lower temperature materialwhich cannot be detected by the SXT but produces strong micr owave free-free emission. This is the first time that such materialis observed in two-sided-l oop type jets. Thus our observations confirm the theoreticalprediction by Yo koyama and Shibata (1996). We detected no coolmaterialat the base of the jets. We also observed an Hα surge which was not associated with an X-ray jet and showed no signatures on the SXT images but was detected with the Nobeyama Radioheliograph. The emission of the microwave surge-associated source was free-free from the chromospheric plasma. Constraints for the surge density were derived.