Vla-Batse Observations Of An Intense Solar Decimetric And Hard X-Ray Burst

We discuss observations of a multiply impulsive solar burst that was detected simultaneously by the Very Large Array (VLA)1 at 20 and 90 cm and by the Burst and Transient Experiment (BATSE) at hard X-ray wavelengths. The flare-associated 20 cm emission consists of two groups of bursts about 4 minutes apart. Hard X-ray emission above 25 keV was detected during both groups of bursts, while 90 cm bursts occurred only during the second and more intense group. VLA snapshot maps at intervals of 1.7 s reveal that the 20 cm burst originates within a relatively compact (theta less-than-or-equal-to 30'') source located above the east limb at a height of h almost-equal-to 1.8 x 10(10) cm (0.26 R.). The 90 cm burst is more extended (theta almost-equal-to 2') and lies at a height of h almost-equal-to 2.2 x 10(10) cm (0.31 R.).Time profiles show that individual burst peaks at 20 and 90 cm are delayed by 3-4 s with respect to those in hard X-rays. The similarity of the time profiles in the two spectral domains suggests a common injection of energetic electrons, while the time delays are consistent with the travel times of electrons which propagate from the chromosphere to the sites of the coronal radio bursts.The VLA brightness temperatures and hard X-ray plasma parameters are combined with multiwavelength radio patrol (RSTN) data in order to constrain the radio emission mechanism. We find that the VLA emission is probably the type III or type IV radiation of electrons trapped in large coronal loops, and that plasma radiation, rather than gyrosynchrotron emission, can explain it.