Diffuse gamma-ray emission toward the massive star-forming region, W40

TL;DR

This study reports the first detection of gamma-ray emission directly from the stellar cluster W40, supporting the idea that young star clusters are significant sources of cosmic rays, with implications for understanding cosmic-ray origins.

Contribution

First detection of gamma-ray emission originating from a stellar cluster itself, not just surrounding regions, highlighting young star clusters as cosmic-ray factories.

Findings

Gamma-ray emission detected with 18sigma significance.

The gamma-ray spectrum has a photon index of 2.49.

The emission is likely hadronic in origin, related to cosmic-ray protons.

Abstract

We report the detection of high-energy gamma-ray signal towards the young star-forming region, W40. Using 10-year Pass 8 data from the Fermi Large Area Telescope (Fermi-LAT), we extracted an extended gamma-ray excess region with a significance of about 18sigma. The radiation has a spectrum with a photon index of 2.49 +/- 0.01. The spatial correlation with the ionized gas content favors the hadronic origin of the gamma-ray emission. The total cosmic-ray (CR) proton energy in the gamma-ray production region is estimated to be the order of 10^47 erg. However, this could be a small fraction of the total energy released in cosmic rays (CRs) by local accelerators, presumably by massive stars, over the lifetime of the system. If so, W40, together with earlier detections of gamma-rays from Cygnus cocoon, Westerlund 1, Westerlund 2, NGC 3603, and 30 Dor C, supports the hypothesis that young star clusters are effective CR factories. The unique aspect of this result is that the gamma-ray emission is detected, for the first time, from a stellar cluster itself, rather than from the surrounding "cocoons".