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 for 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 Westerlund 1 stellar cluster and Kes 41 supernova remnant using > 16 years of data from the Fermi Large Area Telescope (LAT) at energies > 0.8 GeV. We test whether clusters of gamma-ray sources not associated to multiwavelength counterparts are better described by extended emission components. We report the detection of three new extended emission components with soft spectra towards regions of high gas column density in the Galactic plane. One extended component associated with the natal cloud of Kes 41 is statistically preferred over the point source previously reported towards the supernova remnant shell. The other two extended components overlap with neutral gas within ~100 pc from the edge of the Westerlund 1 superbubble. The extended emission may be explained either by mismodeled gas in the interstellar background model or by the local injection of particles. Under the latter hypothesis, explaining the component associated with Kes 41 requires converting ≲ 5% of the supernova remnant energy into accelerated particles, while accounting for the two components near Westerlund 1 requires converting 10−4 of the cluster wind mechanical power into gamma rays. Nevertheless, our results strengthen the evidence for 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 the Fermi LAT. (Abridged)
Related
- Diffuse gamma-ray emission in the vicinity of open cluster Berkeley 87
- Interpreting the γ-ray emission from Westerlund 1: hadronic or leptonic?
- A New Era for Supernova Science with the James Webb Space Telescope
- Core-Collapse Supernova detections from Einstein Telescope within the Milky Way
- The extended globular cluster system of the archetypal "failed galaxy" Dragonfly-44 from deep white-light Hubble Space Telescope imaging
BibTeX
@misc{tibaldo2026extended,
title = {{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}},
author = {L Tibaldo and R Bernet and L Härer and M Lemoine-Goumard and L Mohrmann and G Peron and B Reville and T Vieu},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.10176},
eprint = {2609.10176},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05759387v1},
}
RIS
TY - UNPB
TI - 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
AU - L Tibaldo
AU - R Bernet
AU - L Härer
AU - M Lemoine-Goumard
AU - L Mohrmann
AU - G Peron
AU - B Reville
AU - T Vieu
PY - 2026
DA - 2026/09/09
PB - HAL
DO - 10.48550/arxiv.2609.10176
UR - https://hal.science/hal-05759387v1
AB - There is growing evidence for 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 Westerlund 1 stellar cluster and Kes 41 supernova remnant using > 16 years of data from the Fermi Large Area Telescope (LAT) at energies > 0.8 GeV. We test whether clusters of gamma-ray sources not associated to multiwavelength counterparts are better described by extended emission components. We report the detection of three new extended emission components with soft spectra towards regions of high gas column density in the Galactic plane. One extended component associated with the natal cloud of Kes 41 is statistically preferred over the point source previously reported towards the supernova remnant shell. The other two extended components overlap with neutral gas within ~100 pc from the edge of the Westerlund 1 superbubble. The extended emission may be explained either by mismodeled gas in the interstellar background model or by the local injection of particles. Under the latter hypothesis, explaining the component associated with Kes 41 requires converting ≲ 5% of the supernova remnant energy into accelerated particles, while accounting for the two components near Westerlund 1 requires converting 10^−4 of the cluster wind mechanical power into gamma rays. Nevertheless, our results strengthen the evidence for 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 the Fermi LAT. (Abridged)
ER -