VHE gamma-rays from Westerlund 2 and implications for the inferred energetics

TL;DR

This paper analyzes the gamma-ray emission from Westerlund 2, exploring energetic constraints and possible particle acceleration mechanisms, and discusses the efficiency of converting stellar wind energy into gamma rays.

Contribution

It provides a detailed energetic analysis of gamma-ray production in Westerlund 2, considering different scenarios and wind properties, to understand the system's particle acceleration processes.

Findings

Gamma-ray luminosity is about 10^35 erg/s.

Efficiency of converting kinetic energy into gamma rays is constrained by wind properties.

Implications for particle acceleration mechanisms in stellar clusters.

Abstract

The H.E.S.S. collaboration recently reported the discovery of VHE gamma-ray emission coincident with the young stellar cluster Westerlund 2. This system is known to host a population of hot, massive stars, and, most particularly, the WR binary WR20a. Particle acceleration to TeV energies in Westerlund 2 can be accomplished in several alternative scenarios, therefore we only discuss energetic constraints based on the total available kinetic energy in the system, the actual mass loss rates of respective cluster members, and implied gamma-ray production from processes such as inverse Compton scattering or neutral pion decay. From the inferred gamma-ray luminosity of the order of 10^35 erg/s, implications for the efficiency of converting available kinetic energy into non-thermal radiation associated with stellar winds in the Westerlund 2 cluster are discussed under consideration of either the presence or absence of wind clumping.