Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of Soft X-Ray Emission from Io, Europa and the Io Plasma Torus   We report the discovery of soft (0.25--2 keV) x-ray emission from the
Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma
Torus (IPT). Bombardment by energetic (>10 keV) H, O, and S ions from the
region of the IPT seems the likely source of the x-ray emission from the
Galilean satellites. According to our estimates, fluorescent x-ray emission
excited by solar x-rays, even during flares from the active Sun,
charge-exchange processes, previously invoked to explain Jupiter's x-ray aurora
and cometary x-ray emission, and ion stripping by dust grains fail to account
for the observed emission. On the other hand, bremsstrahlung emission of soft
X-rays from non-thermal electrons in the few hundred to few thousand eV range
may account for a substantial fraction of the observed x-ray flux from the IPT.

24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol