Context. The environs of massive, early-type stars have beeninspected in recent years in the search for sites where particles canbe accelerated up to relativistic energies. Wind regions of massivebinaries that collide have already been established as sources ofhigh-energy emission; however, there is a different scenario formassive stars where strong shocks can also be produced: the bow-shapedregion of matter piled up by the action of the stellar strong wind of arunaway star interacting with the interstellar medium. Aims. We study the bow-shock region produced by a very massive runaway star, BD+433654, to look for nonthermal radio emission as evidence of a relativistic particle population. Methods. We observed the field of BD+433654at two frequencies, 1.42 and 4.86GHz, with the Very Large Array(VLA), and obtained a spectral index map of the radio emission. Results. We have detected, for the first time, nonthermal radio emission from the bow shock of a massive runaway star. Conclusions. After analyzing the radiative mechanisms that canbe at work, we conclude that the region under study could produceenough relativistic particles whose radiation might be detectable byforthcoming gamma-ray instruments, like CTA North. Key words: stars: early-type - stars: individual: BD+433654 - radio continuum: general - infrared: stars
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