  We present a detailed analysis of Jupiter's X-ray (0.2-10 keV) auroral
emissions as observed by XMM-Newton in Nov. 2003 and compare it with that of an
Apr. 2003 observation. We discover the existence of an electron bremsstrahlung
component in the aurorae, which accounts for essentially all the X-ray flux
above 2 keV: its presence had been predicted but never detected for lack of
sensitivity of previous X-ray missions. This bremsstrahlung component varied
significantly in strength and spectral shape over the 3.5 days covered by the
Nov. 2003 observation, displaying substantial hardening of the spectrum with
increasing flux. This variability may be linked to the strong solar activity
taking place at the time, and may be induced by changes in the acceleration
mechanisms inside Jupiter's magnetosphere. As in Apr. 2003, the auroral spectra
below 2 keV are best fitted by a superposition of line emission most likely
originating from ion charge exchange, with OVII playing the dominant role. We
still cannot resolve conclusively the ion species responsible for the lowest
energy lines (around 0.3 keV), so the question of the origin of the ions
(magnetospheric or solar wind) is still open. It is conceivable that both
scenarios play a role in what is certainly a very complex planetary structure.
High resolution spectra of the whole planet obtained with the XMM-Newton RGS in
the range 0.5-1 keV clearly separate emission lines (mostly of Fe) originating
at low latitudes on Jupiter from the auroral lines due to O. These are shown to
possess very broad wings which imply velocities of ~5000 km/s. Such speeds are
consistent with the energies at which precipitating and charge exchanging O
ions are expected to be accelerated in Jupiter's magnetosphere. Overall we find
good agreement between our measurements and the predictions of recent models.
