Investigating Particle Acceleration in the Wolf-Rayet Bubble G2.4+1.4

TL;DR

This paper reports the first detection of non-thermal synchrotron emission from a stellar bubble associated with a WO star, demonstrating that isolated massive stars can accelerate cosmic rays, contributing to Galactic cosmic ray sources.

Contribution

It provides the first observational evidence of non-thermal emission from a single stellar bubble, confirming isolated massive stars as cosmic ray accelerators.

Findings

Detected non-thermal emission with spectral index -0.83

Estimated a few percent of wind kinetic power converts to cosmic rays

Confirmed isolated massive stars as sources of Galactic cosmic rays

Abstract

The supersonic winds produced by massive stars carry a large amount of kinetic power. In numerous scenarios such winds have been proven to produce shocks in which relativistic particles are accelerated emitting non-thermal radiation. Here, we report the first detection of non-thermal emission from a single stellar bubble, G2.4+1.4, associated with a WO star. We observed this source with the uGMRT in Band 4 ($550-850$ MHz) and Band 5 ($1050-1450$ MHz). We present intensity and spectral index maps for this source that are consistent with synchrotron emission (average spectral index, $\alpha = -0.83 \pm 0.10$). The fraction of the available kinetic wind power that is converted into cosmic ray acceleration is estimated to be of the order of a few per cent. This finding constitutes an observational breakthrough and gives new insight on the non-thermal physical processes taking place in the environments of isolated massive stars. In particular, our results show that non-runaway isolated massive stars are capable of accelerating relativistic particles and are therefore confirmed as sources of Galactic cosmic rays.