Detection of nonthermal emission from the bow shock of a massive runaway star

TL;DR

This paper reports the first detection of nonthermal radio emission from the bow shock of a massive runaway star, indicating the presence of relativistic particles and potential gamma-ray emission.

Contribution

It presents the first observational evidence of nonthermal emission from a runaway star's bow shock, expanding understanding of particle acceleration in stellar environments.

Findings

Detected nonthermal radio emission at 1.42 and 4.86 GHz

Spectral index map indicates relativistic particles

Potential gamma-ray emission detectable by future instruments

Abstract

The environs of massive, early-type stars have been inspected in recent years in the search for sites where particles can be accelerated up to relativistic energies. Wind regions of massive binaries that collide have already been established as sources of high-energy emission; however, there is a different scenario for massive stars where strong shocks can also be produced: the bow-shaped region of matter piled up by the action of the stellar strong wind of a runaway star interacting with the interstellar medium. We study the bow-shock region produced by a very massive runaway star, BD+43 3654, to look for nonthermal radio emission as evidence of a relativistic particle population. We observed the field of BD+43 3654 at two frequencies, 1.42 and 4.86 GHz, with the Very Large Array (VLA), and obtained a spectral index map of the radio emission. We have detected, for the first time, nonthermal radio emission from the bow shock of a massive runaway star. After analyzing the radiative mechanisms that can be at work, we conclude that the region under study could produce enough relativistic particles whose radiation might be detectable by forthcoming gamma-ray instruments, like CTA North.