High-energy Processes in the Bubbles of Wolf-Rayet Stars: The case of WR 102

TL;DR

This paper models high-energy processes in the stellar bubble of WR 102, predicting gamma-ray emission and exploring cosmic ray acceleration, with implications for understanding particle acceleration in massive star environments.

Contribution

It presents the first high-energy model for WR 102's bubble, fitting radio data and predicting gamma-ray emission considering both leptonic and hadronic processes.

Findings

Protons may reach PeV energies in the bubble.

Gamma-ray flux predicted is too low for detection.

Relativistic electrons account for 3% of wind kinetic power.

Abstract

Supersonic winds from massive stars carry great amounts of kinetic power and modify the surrounding interstellar medium. Through this interaction a stellar bubble is formed. Theoretical studies and recent observations suggest that the winds of massive stars could be sources of Galactic cosmic rays. The first detection of synchrotron emission from the bubble of a single star was reported, indicating the presence of relativistic electrons. Studying the non-thermal emission from a single massive star can help to better understand the acceleration of particles taking place in massive star clusters. WR 102 is the perfect case of study. In this work, we present the first high-energy model for the bubble of WR 102: G2.4+1.4. We aim at fitting the radio data and predicting gamma-ray emission. We assume that both electrons and protons are accelerated at the wind shock. We applied a classical model for the stellar bubble and adopted a one-zone model for estimating the radiation produced by the relativistic particles near the acceleration region. Additionally, we computed the expected emission from the protons that diffuse to the outer regions of the bubble. Also, we estimated the leptonic and hadronic contributions expected from cosmic rays. We fitted the observations considering that 3% of the wind kinetic power goes into relativistic electrons, and a magnetic field of 250 $\mu$G. The dominant component at high energies is produced by locally accelerated protons reaching the shell. Protons might reach PeV energies in the wind bubble, but the predicted gamma-ray flux is too low to be detectable.