We have modelled the high-energy astrophysics of the inner 200 pc of the
Galaxy with a view to explaining the diffuse, broad-band (radio continuum to
TeV gamma-ray), non-thermal signal detected from this region. Our modelling
pins down the ISM parameters for the environment wherein cosmic ray (CR)
electrons and ions reside in the Galactic centre (GC). We find that the
magnetic field in this region is 100-300 microG, the gas density < 60 cm^-3,
and that a powerful (> 200 km/s) 'super'-wind acts to remove > 95% of the
cosmic rays accelerated in the region before they have time to lose their
energy in situ. The ~ 10^39 erg/s carried away by the GC cosmic ray protons is
precisely enough to energise the ~GeV gamma-ray emission from the Fermi
'bubbles' recently found to extend north and south of the GC out to distances
of ~10 kpc, provided that the bubbles constitute thick targets to the GC
protons and that the situation has reached steady state. In such a situation of
'saturation' the hard, uniform spectrum of the bubbles are explained and
secondary electron synchrotron explains the non-thermal microwave emission
found in WMAP data mirroring the bubbles. Given the very low density of the
bubble plasma ( 5 Gyr. Our
scenario thus has the startling implication that a GC source of nonthermal
particles of time-averaged power 10^39 erg/s has persisted since the youth of
the Galaxy.Comment: 7 pages, 1 figure. Accepted to the Proceedings of the 25th Texas
Symposium on Relativistic Astrophysics (Heidelberg, 2010). References updates
and abstract typo corrected: "100-300 mG" -> "100-300 microG
