The Forty-Minute Period of Jupiter's X-ray Polar Emission

The observation of Jupiter's x-ray auroral emission during the Cassini Jupiter flyby has brought information of prime interest. The High Resolution Camera onboard the Chandra satellite has a pixel size of ~.13 arcsec, which makes it possible to discriminate emission features inside the Jovian polar regions. A ten-hour (one full Jovian rotation) light curve of the northern polar cap region (i.e. a region enclosed by System-3 longitude 160-180° and latitude 60-70°) clearly shows a forty-minute oscillation. This oscillation is shown to be independent of the viewing geometry. Such an oscillation is more speculative for the southern polar cap for which the S/N is much lower than in the North. However, if statistically significant, the fluctuation observed in the southern cap may be in close anticorrelation with the northern cap light curve. This would suggest a bouncing motion of the impinging particles, presumably sulfur and oxygen ions, between the polar cap mirror points. Comparison with HST-STIS far ultraviolet (FUV) observations taken during this Jovian rotation allows us to correlate the x-ray emission with a persistent FUV feature mapping to ~30 RJ in the dayside magnetosphere. This feature shows significant local time variations. However, the sampling of the STIS observations does not permit us to highlight a forty-minute oscillation in the corresponding ultraviolet light curve. Previous STIS spectra favor a high FUV color ratio for the polar cap emission, which is consistent with precipitation of high energy sulfur and oxygen ions.