The 1975.9 Jovian decimetric spectrum

Measurements of the Jovian decimetric radio flux on December 5 and 6, 1975 (1975.9), have been carried out by using the Arecibo radio telescope at four frequencies: 318, 430, 1415, and 2380 MHz. Observed flux values were obtained by comparison with the radio sources 3C18 and 3C459. These flux values were further corrected for the becoming of the Jovian emission about the xenonmagnetic equator, for the antenna-emission polarization angle (a24.5% degree of linear polarization being assumed, since the 318- and 2380-MHz feeds were linearly polarized), and for the antenna-source resolution at 1415 and 2380 MHz. Total flux values of 7.2, 7.4, 6.1, and 7.4 Jy (janskys) were obtained at 318, 430, 1415, and 2380 MHz, respectively. These values represent nearly the largest reported at 318, 430, and 2380 MHz, whereas the 1415-MHz value is among the lowest. Compared to estimates of the synchrotron flux complied by Klein, the 1415- and 2380-MHz fluxes are still rising from minimum values in the 1972 epoch. At 2380 MHz the flux has increased by 34% since the Pioneer 10 encounter at Jupiter. The 2380-MHz beam width has been convoled against brightness distribution models of Jupiter and compared with the Jovian scans. The beam broadening is consistent with the location of the peak synchrotron radiation zone at 1.6R4 (Jovian radii) from the disk center, whereas in 1972, interferometer observations placed the zones at 1.3R4. At 1975.9 the synchrotron spectrum increases toward lower frequencies over the range observed. These result further substantiate the time variability of the synchrotron flux and the flux spectrum, which provides information on changes in the energetic electron processes of energization, loss, and radial diffusion in the inner Jovian magnetosphere