Observational analysis reveals extended gamma-ray emission toward young cluster Berkeley 87, indicating stellar winds actively drive cosmic ray acceleration.
Young massive stellar clusters have been recognized as a significant population of cosmic ray accelerators and gamma-ray sources. We report the detection of extended gamma-ray emission toward the young massive star cluster Berkeley 87 using 18 years of Fermi-LAT data. The emission has an angular extension of 0.36 degree and a photon index of 2.68. To investigate the ambient gas target, we combine CO, EBHIS and Planck data. The total gas mass within the region is ~21.61 × 102M⊙, with an average proton density of ~ 368\ cm⁻³. The hadronic scenario is favored given the dense gas and the cluster’s strong stellar winds. The kinetic energy injection rate from stellar winds in Berkeley 87 exceeds 1.0 × 10³⁶\ erg \ s⁻¹. Considering a CR acceleration efficiency 10−2.0 to 10−2.5, the cluster can supply sufficient energy to power the observed gamma-ray emission. A nearby pulsar, PSR J2021+3651, associated with the Dragonfly pulsar wind nebula and the 4HWC source 4HWC J2021+3650, lies in the same field of view. We also discuss the maximum accelerated proton energy and electron energy density of this pulsar.
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