Detection of extended gamma-ray emission in the vicinity of Cl Danks 1 and 2

TL;DR

This paper reports the detection of extended gamma-ray emission near the Danks 1 and 2 star clusters, indicating these clusters are likely cosmic ray accelerators, with detailed spectral analysis and spatial distribution supporting this conclusion.

Contribution

First detection of extended gamma-ray emission in the G305 region, linking young star clusters to cosmic ray acceleration with spectral and spatial analysis.

Findings

Extended gamma-ray source detected with ~13 sigma significance

Gamma-ray spectrum shows a pion-bump feature consistent with CR interactions

CR radial distribution follows a 1/r profile, supporting continuous injection hypothesis

Abstract

We report the detection of high-energy gamma-ray emission towards the G305 star-forming region. Using almost 15 years of observation data from {\sl Fermi} Large Area Telescope, we detected an extended gamma-ray source in this region with a significance of $\sim 13 \sigma$. The gamma-ray radiation reveals a clear pion-bump feature and can be fitted with the power law parent proton spectrum with an index of $-2.5$. The total cosmic ray (CR) proton energy in the gamma-ray production region is estimated to be the order of $10^{49}\ \rm erg$. We further derived the CR radial distribution from both the gamma-ray emission and gas distribution and found it roughly obeys the $1/r$ type profile, which is consistent with other similar systems and expected from the continuous injection of CRs by the central powerful young massive star cluster Danks 1 or Danks 2 in this region. Together with former detections of similar gamma-ray structures, such as Cygnus cocoon, Westerlund 1, Westerlund 2, NGC 3603, and W40, the detection supports the hypothesis that young massive star clusters are CR accelerators.