Extended gamma-ray emission in the vicinity of the Westerlund 1 massive star cluster and Kes 41 supernova remnant seen by the Fermi Large Area Telescope

Abstract

There is growing evidence of cosmic-ray acceleration in massive stellar clusters. Furthermore, extended gamma-ray emission suggests that particle transport in the vicinity of their sources is influenced by physical processes markedly different from large-scale diffusion in the Milky Way. We characterize extended gamma-ray emission in the direction of the stellar cluster and supernova remnant using more than 16 years of data from the Large Area Telescope (LAT) at energies greater than 0.8 GeV. Westerlund 1 Kes 41 Fermi We tested whether clusters of gamma-ray sources not associated with multiwavelength counterparts are better described by extended emission components and characterized their spatial and spectral properties as well as their correlation with interstellar structures. We report the detection of three new extended emission components with soft spectra toward regions of high gas column density in the Galactic plane. One extended component is associated with the natal cloud of and is statistically preferred over the point source previously reported toward the supernova remnant shell. The other two overlap with neutral gas within ∼100 pc from the edge of the superbubble. The extended emission may be explained by either mismodeled gas in the interstellar background model or the local injection of particles. Under the latter hypothesis, explaining the component associated with requires converting łesssim 5% of the supernova remnant energy into accelerated particles, while accounting for the two components near requires converting 10^-4 of the cluster wind mechanical power into gamma rays. Kes 41 extended components Westerlund 1 Kes 41 Westerlund 1 More detailed physical modeling and more accurate observational constraints are needed to conclude whether the new extended emission components are due to particles that escap from and . Nevertheless, our results strengthen the evidence of gamma-ray emission structures arising at intermediate spatial scales between isolated objects and the large-scale diffuse emission from the interstellar medium. This could explain a part of the soft unassociated Galactic sources detected by ed Westerlund 1 Kes 41 LAT.