Large-scale emission from gamma-ray binaries: the case of LS 5039

Abridged abstract: Context: Gamma-ray binaries hosting a non-accreting neutron star and a massive star exhibit multi-wavelength emission on different spatial scales. The interaction between their winds produces an outflow that can inflate a bubble or form a bow shock as it interacts with the surrounding medium. LS 5039 shows extended (1 pc-scale) X-ray emission that may arise from one of these large-scale structures. Aims: We explain and predict the large-scale emission from LS 5039. Methods: We modelled the thermal and non-thermal emission from five scenarios, representing different evolutionary phases, assuming particle acceleration at the mixed-wind termination shock: three bubble scenarios, treated with a one-zone model, and two bow-shock scenarios, studied with a multi-zone approach. We also investigated the radiation from escaping particles. Results: The extended X-rays are best explained as synchrotron radiation. Some scenarios predict detectable radio emission, while escaping particles may provide a minor steady contribution to the gamma rays in the powerful bow-shock scenario. Escaping protons with energies of 0.1-1 PeV could also inject up to about10 36 erg s-1 into Galactic cosmic rays for optimistic injection luminosities. Conclusions: Gamma-ray binaries can efficiently accelerate particles on large scales, producing broadband emission and 0.1-1 PeV cosmic rays. Our results can guide future multi-wavelength observations to constrain the large-scale interaction, age, and birthplace of LS 5039.