ENA periodicities and their phase relations to SKR emissions at Saturn

Cassini orbits during days 200–366 in 2004 afforded the opportunity to continuously observe energetic neutral atom (ENA) emissions from long range (>50 R S , 1 R S = 60268 km) on Saturn's dawn side. Images of energetic neutral hydrogen (25–55 keV) and oxygen (90–160 keV) were projected onto the noon‐midnight plane, corrected for travel time from Saturn, averaged into half hour time bins and finally averaged into a 60 × 40 R S spatial bin. The time profiles of these bin averages were then subjected to a Lomb periodogram analysis. The H periodogram exhibits a weak periodicity (SNR = 9.1) with a major peak at 10.78 hours and several minor peaks. The O periodogram displays strong periodicities (SNR = 36.2) with a major peak at 10.78 hours and a various secondary peaks. A cross correlation of the SKR signal with the ENA signals reveals that the H signal leads the SKR by 1.46 ± 0.08 hours, while the O signal leads the SKR by 2.21 ± 0.14 hours.