AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 17. Coronal Mass Ejections
Display, Monday, May 31, 1999, 9:20am-6:30pm, Southeast Exhibit Hall

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[17.04] A Microwave Study of Coronal Ejecta

M. R. Kundu, A. Nindos (U. of Maryland), J.-P. Raulin (CRAEE (Mackenzie, INPE, USP, UNICAMP) Inst. Presbiteriano), K. Shibasaki (Nobeyama Radio Obs.), S. M. White (U. of Maryland), N. Nitta (Lockheed Martin Solar \& Astrophysics Lab.), K. Shibata, M. Shimojo (National Astronomical Obs., Tokyo)

Using Nobeyama 17 GHz data, we have studied the radio properties of 19 coronal jets identified in Yohkoh SXT X-ray observations. The radio data provide information on the physical conditions in the jets which complements the data from the X-ray surveys. Microwave emission was associated with the majority of the X-ray jets in our sample. The radio emission typically came from the base or the base and lower part of the jets. We detected radio emission from almost all jets which showed flare-like activity at their bases. The jets which were not associated with radio emission did not show any significant increase in X-ray emission at their bases. The strongest radio emission came from two of the largest jets in our sample. Our data show a general correlation between the X-ray jet fluxes and the associated radio fluxes. The 17 GHz time profiles were gradual and unpolarized, implying that the emission was thermal. In a two-sided-loop jet (July 22, 1992 event) and one anemone-type jet (February 9, 1993 event), the observed microwave fluxes from the lower part of the jets were well above the fluxes calculated from the computed physical parameters of the soft X-ray-emitting material on the basis of thermal free-free emission. We interpret the large discrepancies in terms of the presence of lower temperature material which cannot be detected by the SXT (the SXT is most sensitive to hot plasma above 2 \times 106 K) but which produces strong microwave free-free emission. This is the first time that such material has been observed in two-sided-loop type jets. We also observed motion of a jet-associated microwave source with a velocity of 55 km/sec. The microwave motion occurred after the appearance of the X-ray jet. There is clear evidence that the microwave emission of that source was associated with the jet and not with the associated small flare.

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