Investigating the Gamma-Ray Emission from Explosive Dispersal Outflows with Fermi-LAT

TL;DR

The study tests whether explosive dispersal outflows (EDOs) in massive star-forming regions are gamma-ray sources and contributors to the Galactic cosmic-ray budget, using 16 years of Fermi-LAT data in the $0.2$--$500$ GeV band. Analyzing seven Galactic EDOs, the authors identify GeV emission from three sources (DR21, G34.26+0.15, G5.89-0.39), with DR21 the most significant. For DR21, the spectrum is consistent with a power law with an exponential cutoff, and the gamma-ray luminosity in the $0.1$--$500$ GeV range is about $2e35$ erg s^-1, implying a particle-acceleration efficiency up to about 18% relative to the outflow kinetic energy. These results show that EDOs can span a wide range of gamma-ray luminosities and efficiencies and may contribute non-negligibly to the Galactic CR budget, motivating further searches and multiwavelength characterization of their environments.

Abstract

We present the first systematic study of explosive dispersal outflows (EDOs) as potential sources of high-energy emission in the Milky Way. EDOs are energetic outflows produced during dynamical interactions in young, massive star-forming regions, and their physical conditions make them promising environments for cosmic-ray acceleration. Using 16 years of $0.2$--$500$ GeV Fermi-LAT observations, we study the gamma-ray properties of seven EDOs. Three EDOs, DR21, G34.26$+$0.15, and G5.89$-$0.39 show spatially coincident GeV emission, while the remaining systems yield non-detections. Among the sample, DR21 stands out as the brightest candidate, with a detection significance $\geq 40σ$. Its spectrum is well described by a power law with an exponential cutoff, and the integrated luminosity in the $0.1$--$500$ GeV band is $L_γ\simeq 2\times10^{35}\ \mathrm{erg\ s^{-1}}$. When compared with the outflow's estimated kinetic energy, the inferred cosmic-ray acceleration efficiency is $\leq 18\%$, consistent with values for shocks in dense molecular environments. The energetics and morphology support an association between the DR21 molecular outflow and the observed gamma rays. Our results demonstrate that EDOs span a wide range of gamma-ray luminosities and efficiencies, suggesting they may contribute to the Galactic cosmic ray budget. This motivates searches for additional EDOs and improved multiwavelength characterization of their environments.