ENA periodicities and their phase relations to SKR emissions at Saturn

Abstract

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.