Electron cooling times. Left: default case (see Table 1). The broad grey line is the sum of all the components shown in colour. For a description of the photon fields for IC scattering, see the text. Right: range of plausible cooling times for synchrotron radiation (orange), bremsstrahlung (green), and the sum of all IC components (blue), resulting from a cluster photon field energy density of U_cl = 3 − 180 eV cm⁻³, a density inside the superbubble of n_int = 0.02 − 0.1 cm⁻³, an effective cluster temperature of T_eff = 10 000 − 50 000 K, a magnetic field of B = 1 − 10 μG, and an enhancement of the diffuse stellar and dust emission by a factor 1−3. The enhancement of the diffuse component is motivated by the proximity to the cluster and increased dust density in the region, compared to the standard ISM. The inset shows the behaviour in the TeV-band in more detail, highlighting the loss-time scaling with energy. The default case (broad grey line) shows a behaviour that would require diffusion close to the Kraichnan regime (D ∼ E^1/2) to reproduce an energy-independent morphology.