Speaker
Description
Recently, the Large High-Altitude Air Shower Observatory (LHAASO) collaboration reported ultra-high-energy gamma-rays from six microquasar systems. For five of these, the emission exceeds $100$ TeV, making microquasars promising Galactic PeVatrons. In this work, we investigate whether gamma-rays around $100$ TeV can originate from hadronic interactions of accelerated cosmic rays with the ambient medium and estimate the contribution of these sources to the CR proton knee. Two transport scenarios are considered: one in which particle transport around the source is dominated by advection, and another in which it is dominated by diffusion, with the diffusion coefficient reduced with respect to the Galactic value. In both scenarios, the diffusion coefficient matches the Galactic value at large distances from the source. We also explore two injection models: continuous cosmic-ray injection over the entire lifetime of the source, and intermittent injection during periodic outbursts. We find that in both advection and diffusion scenarios, hadrons alone cannot fully explain the observed emission, allowing us to place upper limits on the hadronic fraction of the flux. Finally, we estimate the contribution of these sources to the Galactic cosmic-ray spectrum; this quantity strongly depends on source age and injection history.
