Multi-frequency total flux measurements of Jupiter’s synchrotron radiation in 2007

Total flux densities of Jupiter’s synchrotron radiation (JSR) were regularly observed at frequencies of 325 and 785MHz with the Iitate Planetary Radio Telescope (IPRT) from May to July 2007 and at 2.3GHz with the 34-m radio telescope at the National Institute of Information and Communications Technology (NICT) in June. These observations were made as part of a simultaneous spectrum and interferometer observation campaign. This paper describes the results of the absolute total flux measurements made by the single dish telescopes. Since the frequency range below 1GHz is not often used for JSR observations, except for campaign-based observations, regular observation in this low frequency range is expected to provide new information on the dynamic behavior of Jupiter’s radiation belt. The receiver system of IPRT has a function to measure the on-site gain and noise temperature of the receiver, and it can compensate for instrumental fluctuations. Besides the observation of JSR itself, the galactic background flux just behind Jupiter was also observed in order to obtain the absolute flux density of JSR. The JSR observations have a short-term variation with a time scale of a few days and amplitude of ±20–30%. The variation does not coincide with the solar F10.7 flux. This implies that an enhanced radial diffusion, which is driven by the neutral wind in the upper atmosphere, is not responsible for the time variation in JSR. Some enhancements in JSR suggest the time response to changes in solar wind activity. The characteristics of the short-term variation in the low-frequency range would imply that various mechanisms contribute to it.