Analysis of Saturn kilometric radiation near a source center

The Cassini spacecraft flew very near a source region of Saturn kilometric radiation (SKR) on day 73 of 2008, the second known encounter with a source region at high latitude. The radio and plasma wave instrument, Radio and Plasma Wave Science, observed intense kilometric emission in the extraordinary X mode, ordinary O mode, and Z mode. The electron low-energy spectrometer obtained a phase space distribution of sufficient energy and pitch angle resolution to allow growth rate calculations. There is evidence of a shell-like electron plasma distribution that is unstable to the growth of SKR via the cyclotron maser instability. The growth rates calculated are adequate to explain the observed X and Z mode emission, but nonlinear effects are required to explain the large O mode gain (as is true for terrestrial observations). Narrowband emission, also present at the time, could also explain both the Z mode and the O mode. We present the results for comparison with a previously reported source region encounter and with similar observations at Earth auroral kilometric source regions.