Diffuse gamma-ray emission in the vicinity of young star cluster Westerlund 2

TL;DR

This study analyzes Fermi-LAT data revealing extended gamma-ray emission near Westerlund 2, suggesting that accelerated protons interacting with ambient gas produce the observed gamma rays, highlighting star clusters as cosmic-ray accelerators.

Contribution

First detection of extended gamma-ray emission around Westerlund 2, linking star cluster activity to cosmic-ray acceleration and diffuse gamma-ray production.

Findings

Extended gamma-ray emission with a hard spectrum from 1 GeV to 250 GeV.

Star cluster Westerlund 2 likely accelerates particles responsible for gamma-ray emission.

Estimated relativistic particle energy budget around 10^50 erg.

Abstract

We report the results of our analysis of the publicly available data obtained by the Large Area Telescope (LAT) on board of the Fermi satellite towards the direction of the young massive star cluster Westerlund 2. We found significant extended gamma-ray emission in the vicinity of Westerlund 2 with a hard power-law energy spectrum extending from 1 GeV to 250 GeV with a photon index of 2.0 +/- 0.1. We argue that amongst several alternatives, the luminous stars in Westerlund 2 are likely sites of acceleration of particles responsible for the diffuse gamma-ray emission of the surrounding interstellar medium. In particular, the young star cluster Westerlund 2 can provide sufficient non-thermal energy to account for the gamma-ray emission. In this scenario, since the gamma-ray production region is significantly larger than the area occupied by the star cluster, we conclude that the gamma-ray production is caused by hadronic interactions of the accelerated protons and nuclei with the ambient gas. In that case, the total energy budget in relativistic particles is estimated of the order of 1e50 erg.