Low- to middle-latitude X-ray emission from Jupiter

Details Low- to middle-latitude X-ray emission from Jupiter Low- to middle-latitude X-ray emission from Jupiter

Nov 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006jgra..11111225b&link_type=abstract

Journal of Geophysical Research, Volume 111, Issue A11, CiteID A11225

Astronomy and Astrophysics

Astrophysics

9

Planetary Sciences: Comets And Small Bodies: Atmospheres (1060), Planetary Sciences: Comets And Small Bodies: Magnetospheres (2756), Planetary Sciences: Solar System Objects: Jupiter, Solar Physics, Astrophysics, And Astronomy: X-Rays, Gamma Rays, And Neutrinos

Scientific paper

The Chandra X-ray Observatory (CXO) observed Jupiter during the period 24-26 February 2003 for ~40 hours (4 Jupiter rotations), using both the spectroscopy array of the Advanced CCD Imaging Spectrometer (ACIS-S) and the imaging array of the High-Resolution Camera (HRC-I). Two ACIS-S exposures, each ~8.5 hours long, were separated by an HRC-I exposure of ~20 hours. The low- to middle-latitude nonauroral disk X-ray emission is much more spatially uniform than the auroral emission. However, the low- to middle-latitude X-ray count rate shows a small but statistically significant hour angle dependence and depends on surface magnetic field strength. In addition, the X-ray spectra from regions corresponding to 3-5 gauss and 5-7 gauss surface fields show significant differences in the energy band 1.26-1.38 keV, perhaps partly due to line emission occurring in the 3-5 gauss region but not the 5-7 gauss region. A similar correlation of surface magnetic field strength with count rate is found for the 18 December 2000 HRC-I data, at a time when solar activity was high. The low- to middle-latitude disk X-ray count rate observed by the HRC-I in the February 2003 observation is about 50% of that observed in December 2000, roughly consistent with a decrease in the solar activity index (F10.7 cm flux) by a similar amount over the same time period. The low- to middle-latitude X-ray emission does not show any oscillations similar to the ~45 min oscillations sometimes seen from the northern auroral zone. The temporal variation in Jupiter's nonauroral X-ray emission exhibits similarities to variations in solar X-ray flux observed by GOES and TIMED/SEE. The two ACIS-S 0.3-2.0 keV low- to middle-latitude X-ray spectra are harder than the auroral spectrum and are different from each other at energies above 0.7 keV, showing variability in Jupiter's nonauroral X-ray emission on a timescale of a day. The 0.3-2.0 keV X-ray power emitted at low to middle latitudes is 0.21 GW and 0.39 GW for the first and second ACIS-S exposures, respectively. We suggest that X-ray emission from Jupiter's disk may be largely generated by the scattering and fluorescence of solar X rays in its upper atmosphere, especially at times of high incident solar X-ray flux. However, the dependence of count rate on surface magnetic-field strength may indicate the presence of some secondary component, possibly ion precipitation from radiation belts close to the planet.

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