X-ray emission from Saturn

Astrophysics, abstract
astro-ph/0401270

From: Jan-Uwe Ness [view email]

Date: Wed, 14 Jan 2004 15:16:44 GMT   (639kb)

Authors:
J.-U. Ness (1),
J.H.M.M. Schmitt (1),
S.J. Wolk (2),
K. Dennerl (3),
V. Burwitz (3) ((1) Hamburger Sternwarte, Universitaet Hamburg, Germany, (2) Chandra X-ray Center, Harvard-Smithsonian Center for Astrophysics, Cambridge, USA, (3) Max-Planck-Institut fuer extraterrestrische Physik, Garching, Germany)

Comments: 10 pages, 6 figures, accepted for publication in A&A

We report the first unambiguous detection of X-ray emission originating from
Saturn with a Chandra observation, duration 65.5 ksec 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 +- 0.2) 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 degrees, 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 10^-15 erg/cm^2/s (in the
energy interval 0.1-2keV), which corresponds to an X-ray luminosity of 8.7
10^14 erg/s. A combination of scatter processes of solar X-rays requires a
relatively high albedo favoring internal processes, but a definitive
explanation remains an open issue.

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