And then they were two: Detection of non-thermal radio emission from the bow shocks of two runaway stars

Winds from massive stars have recently been deemed promising sites for investigating relativistic particle acceleration. Particularly, the resulting bow shock interaction of winds runaway with interstellar matter has observed at multiple wavelengths. Here we investigate O4If star, BD+433654, which is, so far, only one proven to radiate both thermally and non-thermally radio frequencies. We also consider NGC7635 as a candidate examine its apex indications thermal non-thermal emission. sources VLA 4-8 GHz 8-12 GHz, Effelsberg telescope GHz. analysed data telescopes individually combined, obtained their spectral index maps calculated Spectral Energy Distributions. present first high-resolution emission NGC7635. find that emit in regime, clearest evidence Our results are less conclusive becomes weaker fainter higher extend previous BD+433654 Modelling our shows accelerated electrons wind termination plausible source emission, but energetics arguments suggest any X-ray $\gamma$-ray could be significantly below existing upper limits. Enhanced synchrotron compressed Galactic cosmic rays radiative explain not Non-detection point-like puts an limit on mass-loss rate star is lower than values quoted literature. [abridged]