The non-thermal superbubble in IC 10: the generation of cosmic ray
  electrons caught in the act
  Superbubbles are crucial for stellar feedback, with supposedly high (of the
order of 10 per cent) thermalization rates. We combined multiband radio
continuum observations from the Very Large Array (VLA) with Effelsberg data to
study the non-thermal superbubble (NSB) in IC 10, a starburst dwarf irregular
galaxy in the Local Group. Thermal emission was subtracted using a combination
of Balmer H$\alpha$ and VLA 32 GHz continuum maps. The bubble's non-thermal
spectrum between 1.5 and 8.8 GHz displays curvature and can be well fitted with
a standard model of an ageing cosmic ray electron population. With a derived
equipartition magnetic field strength of $44\pm 8 \rm\mu G$, and measuring the
radiation energy density from Spitzer MIPS maps as $5\pm 1\times 10^{-11} \rm
erg\, cm^{-3}$, we determine, based on the spectral curvature, a spectral age
of the bubble of $1.0\pm 0.3 \rm Myr$. Analysis of the LITTLE THINGS HI data
cube shows an expanding HI hole with 100 pc diameter and a dynamical age of
$3.8\pm 0.3 \rm Myr$, centred to within 16 pc on IC 10 X-1, a massive stellar
mass black hole ($M > 23 M_\odot$). The results are consistent with the
expected evolution for a superbubble with a few massive stars, where a very
energetic event like a Type Ic supernova/hypernova has taken place about 1 Myr
ago. We discuss alternatives to this interpretation.
