Two-component $γ$-Ray Structure from the CR Sources

Abstract

With the advent of a new generation of observational experiments and the accumulation of data, an increasing number of cosmic-ray sources have been found to exhibit pronounced two-component structures in their gamma-ray spectra above GeV energies. To investigate whether these structures share a common physical origin, we conduct a statistical study of sources exhibiting such features using a two-component model of cosmic-ray sources and examine their gamma-ray emission mechanisms. We find that the ambient environment significantly affects the spectral morphology. Sources located in low-density environments but surrounded by dense molecular clumps exhibit two clearly separated spectral peaks. In contrast, sources embedded in dense environments with additional dense molecular clumps nearby retain two-component spectral features, but the components overlap more smoothly, with the high-energy component appearing primarily as a relatively broad shoulder rather than a distinct peak. Our results lend further support to a physical picture in which high-energy cosmic rays are predominantly supplied by local sources, whereas low-energy cosmic rays arise mainly from the collective contribution of sources in other regions of the Galaxy. We also calculate the neutrino spectra of these sources, providing theoretical predictions for future tests of the model through observations of point-source and diffuse neutrino emission.