2015MNRAS.447L...1H

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 Hα and VLA 32GHz continuum maps. The bubble's non-thermal spectrum between 1.5 and 8.8GHz 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±8µG, and measuring the radiation energy density from Spitzer MIPS maps as 5±1x10^–11erg/cm3, we determine, based on the spectral curvature, a spectral age of the bubble of 1.0±0.3 Myr. Analysis of the LITTLE THINGS H i data cube shows an expanding H i hole with 100 pc diameter and a dynamical age 3.8±0.3 Myr, centred to within 16 pc on IC 10 X-1, a massive stellar mass black hole (M > 23M_☉). 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.