Non-thermal emission from microquasar jets: The case of GRS 1915+105

Abstract

Microquasars (μQs) represent a prominent population of Galactic sources, from which broadband non-thermal emission was detected. At present, the potential of μQs as sources of gamma-ray emission is poorly understood and constrained. In most cases, even the power of μQ jets remains largely uncertain, and this hinders the study of gamma-ray generation in these sources. Using observational data obtained in the radio band, we derive an estimate of the jet power in one of the most famous Galactic μQ, in GRS 1915+105. Compared to other studies of this subject, we additionally consider constraints related to the energy dissipated at internal shocks in the jet, the conditions at which are obtained using properties of the radio blobs detected in the jets. We show that even if one subtracts the rest-energy of matter in the jet, the jet power in this source should be very high, ${10}^{39}\mathrm{erg}{s}^{-1}$, or even higher. The properties of the detected radio emission favor jets with a Gauss-strength magnetic field at parsec distances from the black hole. Such a strong magnetic field should suppress inverse Compton (IC) emission from relativistic electrons, at least from parsec-scale jet. On the other hand, this strong magnetic field makes μQ jets perfect proton accelerators. If present, protons should easily be accelerated in the ultra-high-energy regime. However, due to a diluted target, protons should not lose a notable fraction of their energy in the jet, injected into the interstellar medium at the jet termination. This should significantly enhance the density of cosmic rays in the vicinity of GRS 1915+105. This may manifest itself as an extended gamma-ray source or as several compact sources if the target gas has a highly inhomogeneous distribution. This analysis has direct implication for studying Galactic μQ with such gamma-ray observatories as LHAASO, CTA, and SWGA in the next decades.