Non-thermal microwave radiation from Jupiter.
Observations of the radio flux from Jupiter have been made at 22-cm and 68-cm wave lengths, using the NRAO 85-foot reflector. The mean flux observed at 22 cm was about 6(10-26) (wm-2) m-2 (c/s)-' during the month of May, 1959. The mean flux at 68 cm on May 26 and 27, 1959, was about 13(10-26) (wm-2) m-2(c/s)-'. The black- body disk temperatures required to produce the observed fluxes, 30000K. and 70,0000K., approximately, are too high to be plausible. Flux measurements at 68 cm during the period July 20-30, 1959, have given a less certain flux density value of 5(10-28) (wm-2) m-2 (c/s)-'. The observed fluxes are combined with the data of other observers to show that Jupiter is, in fact, emitting a non-thermal spectrum with flux proportional to X+~2, approximately. An observational search for variations in the flux is discussed. High-sensitivity monitoring of the planet at 440 mc showed no statistically significant short period variations in flux during two nights of observing. An extensive set of observations at 22 cm suggests that variations of the order of 30 per cent occur in the flux in times of the order of days. There is no statistically significant correlation between the apparent variations and plane~ary rotation. It is proposed that the radiation originates as synchrotron radiation from relativistic particles trapped in the Jovian magnetic field, a situation similar to the terrestrial Van Allen belts. A Jovian field of 5 gauss and a total number of particles 106 times greater than in the terrestrial system will suffice to explain the observations. National Radio A stronomy Observatory Green Bank, W. Va.
The Astronomical Journal
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