Synthesis of magnetospheric radio emissions during and after the Jupiter/SL-9 collision

Abstract

A worldwide network of ground-based and spaced-based radiotelescopes monitored the continuum emission of Jupiter from millimetric to kilometric wavelengths throughout the SL-9 impacts in July 1994. Within 2 days of the first impact, an increase of flux density was detected and confirmed by many observatories at wavelengths from 3 to 90 cm. The increase involved only the synchrotron emission from the energetic electrons trapped in the Jovian radiation belts. At decameter and kilometer wavelengths, normally from radio sources located in the polar regions, no abnormal emission can be associated with certainty with the impacts. At short centimeter and millimeter wavelengths a search was made for impact-associated changes in Jupiter's deep atmosphere, but no detections have been reported and confirmed. The present knowledge of the synchrotron radio emission from the Jovian radiation belts is reviewed and the changes which occurred during and after the collision are commented on. During the week of cometary impacts, the synchrotron flux density increased, depending on the wavelength, by 10–40% and the radio spectrum hardened. Following the week of impacts, the flux density decreased at all wavelengths, more rapidly at 36–90 cm than at 6–22 cm. The observed decline was not a simple exponential decay, and the timescale was more than 100 days at 6–20 cm and less than 30 days at 36–90 cm. The beaming curve was flattened and distorted during and after the impacts, with long-lasting enhancements localized in longitude. Two-dimensional images show that the belts became brighter than before the impacts, and they remained bright at least one week after the first impact. The increase of brightness at the magnetic equator was concentrated in a limited range of longitude, from ≈80 to ≈300°. The radial distance of the peak intensity decreased over that week. Images in 3-D, constructed from observations with the Australia Telescope Compact Array, reveal distinct brightenings confined in longitude that can be attributed to the longitudes of individual impacts or group of impacts.