An upper limit of the number and energy of electrons accelerated at an extended coronal shock wave

Type II radio emission is the most direct signature of extended shock waves in the solar corona, and a prime example of electron acceleration at a shock. Yet, the energetics of these electrons is poorly known. On 1996 August 19 and 1997 October 07 type II bursts were observed in association with flares behind the solar limb. While Earth-orbiting X-ray detectors aboard GOES and the Compton Gamma-Ray Observatory did not register emission above background, the Ulysses spacecraft, which had the candidate active region in its field of view, saw a major burst during the 1996 event. We use this peculiar configuration to infer the energetics of electrons accelerated in the low corona from the Ulysses observations, and to derive upper limits of the number and energy content of shock-accelerated electrons from the thresholds of the Earth-orbiting detectors. The inferred upper limit is similar to electron numbers estimated for large particle events at 1 AU, but the fluxes and energy fluxes of shock-accelerated electrons are much smaller than those required to produce a conspicuous hard X-ray burst.