Attenuation of LHAASO PeVatrons by the Interstellar Radiation Field and Cosmic Microwave Background Radiation

Abstract “PeVatrons” refer to astrophysical sources capable of accelerating particles to energies around 10 15 electron volts and higher, potentially contributing to the cosmic-ray spectrum in the knee region. Recently, the Large High Altitude Air Shower Observatory (LHAASO) has discovered a large number of PeVatrons, allowing us to investigate in greater depth the contributions of these sources to cosmic rays above the knee region. However, high-energy gamma rays undergo attenuation due to interactions with the interstellar radiation field and cosmic microwave background radiation, requiring corrections to restore the true spectral characteristics at the source. In this study, using the interstellar radiation field model extracted from the galprop code, we quantitatively calculated the spectral absorption effects of PeV sources listed in the first LHAASO source catalog, with some sources showing absorption reaching ∼30% at 100 TeV and ∼80% at 3 PeV. We also calculated the high-energy gamma-ray absorption effects of Galactic microquasars, which are potential PeVatrons. By calculating the absorption effects, it will help differentiate the radiation mechanisms of the acceleration sources, to investigate whether they are the origins of high-energy cosmic rays.