Gamma-rays from Wolf-Rayet stellar winds
A. Inventar, G. Peron, S. Recchia, S. Gabici
TL;DR
The paper addresses whether winds from a single Wolf-Rayet star can generate detectable gamma-ray emission via wind termination shocks and hadronic interactions. It assembles wind parameter measurements and Gaia distances for 108 WR stars, computes $L_w=(1/2)\dot M u_w^2$ and ranks stars by $L_w/d^2$ to estimate gamma-ray flux, then cross-matches with gamma-ray catalogs (4FGL, HGPS, 1LHAASO) within ~30 pc to identify candidates. A hadronic emission model with $F_ _gamma \approx \frac{\eta L_w}{4\pi d^2}\left(\frac{\tau_{\rm res}}{\tau_{pp\rightarrow\pi^0}}\right)$ and a density– and confinement-dependent parameter $\kappa$ is used to connect wind power to observed gamma rays, with spectra modeled as $Q(E)\propto E^{-\alpha}$ broken at $E_b$ due to escape. Four WR stars (WR 114, WR 111, WR 14, WR 110) emerge as plausible gamma-ray associations, with $\kappa$ values spanning from order unity to about 12, supporting the idea that WR winds constitute a distinct population of gamma-ray emitters; however, the results depend sensitively on ambient gas density and CR transport, and future work should broaden the WR/O-star census and improve environmental density estimates.
Abstract
Gamma-ray observations of young star clusters have recently provided evidence for particle acceleration occurring at stellar wind termination shocks, fueled by the mechanical energy of stellar winds from massive stars. In this work, we explore the possibility that the wind from a single powerful star, whether isolated or part of a cluster, can alone provide sufficient energy to generate gamma-ray emission detectable by current instruments. This scenario is particularly relevant given that a significant fraction of Wolf-Rayet (WR) stars are not found within clusters. To investigate this, we compiled a large sample of WR stars and ranked them based on their wind luminosity divided by the square of their distance, a proxy for their potential gamma-ray flux. We then searched for spatial coincidences between the most promising candidates and cataloged gamma-ray sources. This analysis leads us to propose associations between the stars WR14, WR110, WR111, and WR114 and several unidentified gamma-ray sources. These results suggest that WR stellar winds could represent a distinct and previously unrecognized population of gamma-ray emitters.