Acceleration of electrons at type II shock fronts and production of shock-accelerated type III bursts

We present evidence of electron acceleration by type II-burst-emitting shoc ks in the corona. Some of the electrons travel outward along open magnetic field lines and produce "shock-accelerated type III bursts" (or SA type III bursts) along their paths, The SA type III bursts are evident in dynamic s pectra that cover part or all of the range from metric to kilometric wavele ngths. The unique feature of our observations is the complete or near-compl ete frequency coverage from about 2 GHz to < 0.1 MHz, that is, <less than o r similar to> 1.01 Ro to 1 AU. A sample of eight events is presented. All w ould be classified as "shock accelerated events" at hectometric wavelengths , as first defined by Cane et al, [1981], Our complete spectra frequently s how several to many type III-like bursts emanating from near the type II bu rst toward low frequencies, with no trace of emission at frequencies higher than that of the type II burst, The drift rates of these SA type III burst s are similar to those of normal type III bursts, and the exciting electron s have speeds of order 0.1c to 0.2c, or energies of 3-10 keV and higher. Th eir intensity at hectometer wavelengths is similar to that of normal type I II bursts. They often persist to the lowest frequencies observable, near th e local plasma frequency at 1 AU, In most of the events examined, there wer e no microwave bursts from the low corona whose intensity profiles were sim ilar to the hectometric profiles. We therefore conclude that these SA type III bursts originate in type II shocks and are caused by energetic electron s accelerated at the shocks. Of the eight events analyzed, three contain on ly SA type III bursts. For the remainder, normal type III bursts predominat e initially, followed by SA type III bursts later in the event. We emphasiz e the need for spectra with near-continuous coverage, especially from decam etric to kilometric wavelengths, to identify SA type III bursts unambiguous ly and to distinguish between the contributions of normal and SA type III b ursts.