X-ray emission from Saturn

We report the first unambiguous detection of X-ray emission originating from Saturn with a Chandra observation, duration 65.5 ks with ACIS-S3. Beyond the pure detection we analyze the spatial distribution of X-rays on the planetary surface, the light curve, and some spectral properties. The detection is based on 162 cts extracted from the ACIS-S3 chip within the optical disk of Saturn. We found no evidence for smaller or larger angular extent. The expected background level is 56 cts, i.e., the count rate is $(1.6\,\pm\,0.2)\times 10^{-3}$ cts/s. The extracted photons are rather concentrated towards the equator of the apparent disk, while both polar caps have a relative photon deficit. The inclination angle of Saturn during the observation was ~$-27^\circ$, so that the northern hemisphere was not visible during the complete observation. In addition, it was occulted by the ring system. We found a small but significant photon excess at one edge of the ring system. The light curve shows a small dip twice at identical phases, but rotational modulation cannot be claimed at a significant level. Spectral modeling results in a number of statistically, but not necessarily physically, acceptable models. The X-ray flux level we calculate from the best-fit spectral models is ~$6.8\times 10^{-15}\mbox{\,erg\,cm}^{-2}\mbox{\,s}^{-1}$ (in the energy interval 0.1–2 keV), which corresponds to an X-ray luminosity of ~$8.7\times 10^{14}\mbox{\,erg}\mbox{\,s}^{-1}$. A combination of scatter processes of solar X-rays require a relatively high albedo favoring internal processes, but a definitive explanation remains an open issue