Search for signatures of outflow interaction around Cygnus X-3

Abstract Cygnus X-3 is a microquasar hosting a Wolf–Rayet star, recently identified as a Galactic PeVatron and a potential ULX source. We analyzed high-resolution H i data to search for interstellar medium interaction signatures across all proposed distances. We identify a candidate H i cavity of ~7 arcmin at a local standard of rest velocity corresponding to a distance of d ≃ 7.7 kpc. Its morphology is compatible with a Wolf–Rayet wind bubble, although such an association depends critically on the system actual distance. However, the H i absorption spectrum imposes a lower limit of d ≳ 9.2 kpc, disfavouring a physical association between the cavity and Cygnus X-3 and placing this microquasar in a distant, low-density Galactic environment. The resulting larger distance increases the intrinsic luminosity of the system, rendering it consistent with recent interpretations of Cygnus X-3 as a persistent ULX source, naturally accounting for the lack of detectable large-scale ISM interaction, and providing additional constraints on particle acceleration models. Our findings are consistent with recent reports of ultra-high-energy emission, favouring scenarios in which the reported PeV emission originates in compact regions close to the binary, where target densities are high, rather than from extended wind or jet termination shocks in the interstellar medium.