Letter to the Editor

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

¹ Instituto Argentino de Radioastronomía, CCT-La Plata (CONICET), C.C.5, 1894 Villa Elisa, Argentina e-mail: [pbenaglia;cperi]@fcaglp.unlp.edu.ar, [romero;anabella]@iar-conicet.gov.ar
² Facultad de Cs. Astronómicas y Geofísicas, UNLP, Paseo del Bosque s/n, 1900 La Plata, Argentina
³ Departamento de Física (EPS), Universidad de Jaén, Campus Las Lagunillas s/n, Edif. A3, 23071 Jaén, Spain e-mail: jmarti@ujaen.es

Received: 18 June 2010
Accepted: 17 July 2010

Abstract

Context. 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.

Aims. 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.

Methods. 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.

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 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.