A model for high-mass microquasar jets under the influence of a strong stellar wind

E. Molina, S. del Palacio, and V. Bosch-Ramon.

Serie: Trabajos publicados del IAR ; no. 1514

Resumen: Context. High-mass microquasars (HMMQs) are systems from whichrelativistic jets are launched. At the scales of several times thebinary system size, the jets are expected to follow a helical pathcaused by the interaction with a strong stellar wind and orbital motion.Such a trajectory has its influence on the non-thermal emission of thejets, which also depends strongly on the observing angle due to Dopplerboosting effects.
Aims: We explore how the expected non-thermalemission of HMMQ jets at small scales is affected by the impact of thestellar wind and the orbital motion on the jet propagation.
Methods: We studied the broadband non-thermal emission, from radio togamma rays, produced in HMMQ jets up to a distance of several orbitalseparations, taking into account a realistic jet trajectory, differentmodel parameters, and orbital modulation. The jet trajectory is computedby considering momentum transfer with the stellar wind. Electrons areinjected at the position where a recollimation shock in the jets isexpected due to the wind impact. Their distribution along the jet pathis obtained assuming local acceleration at the recollimation shock, andcooling via adiabatic, synchrotron, and inverse Compton processes. Thesynchrotron and inverse Compton emission is calculated taking intoaccount synchrotron self-absorption within the jet, free-free absorptionwith the stellar wind, and absorption by stellar photons via pairproduction.
Results: The spectrum is totally dominated by the jetover the counter-jet due to Doppler boosting. Broadband emission frommicrowaves to gamma rays is predicted, with radio emission being totallyabsorbed. This emission is rather concentrated in the regions close tothe binary system and features strong orbital modulation at highenergies. Asymmetric light curves are obtained owing to the helicaltrajectory of the jets.
Conclusions: The presence of helicalshaped jets could be inferred from asymmetries in the light curves,which become noticeable only for large jet Lorentz factors and lowmagnetic fields. Model parameters could be constrained if accuratephase-resolved light curves from GeV to TeV energies were available. Thepredictions for the synchrotron and the inverse Compton radiation arequite sensitive of the parameters determining the wind-jet interactionstructure