On the nature of the AGILE galactic transient sources

Abstract

Context. The Italian gamma-ray satellite AGILE has recently reported the detection of some variable high-energy sources likely of galactic origin. These sources do not have any obvious counterpart at lower energies. Aims. We propose that these sources are produced in proton-dominated jets of galactic microquasars. Methods. We develop a model for microquasar jets that takes into account both primary leptons and protons and all relevant radiative processes, including secondary particle emission and gamma-ray attenuation due to pair creation in the jet. Results. We obtain spectral energy distributions that correspond to what is observed by AGILE, with most of the power concentrated between 100 MeV and 10 GeV and reaching luminosities of 1034-35 erg s-1. We make detailed spectral predictions that can be tested by the Fermi gamma-ray telescope in the immediate future. Conclusions. We conclude that hadronic jets in galactic accreting sources can be responsible for the variable unidentified gamma-ray sources detected by AGILE.