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

Abstract

Context. High-mass microquasars (HMMQs) are systems from which relativistic jets are launched. At the scales of several times the binary system size, the jets are expected to follow a helical path caused by the interaction with a strong stellar wind and orbital motion. Such a trajectory has its influence on the non-thermal emission of the jets, which also depends strongly on the observing angle due to Doppler boosting effects. Aims. We explore how the expected non-thermal emission of HMMQ jets at small scales is affected by the impact of the stellar wind and the orbital motion on the jet propagation. Methods. We studied the broadband non-thermal emission, from radio to gamma rays, produced in HMMQ jets up to a distance of several orbital separations, taking into account a realistic jet trajectory, different model parameters, and orbital modulation. The jet trajectory is computed by considering momentum transfer with the stellar wind. Electrons are injected at the position where a recollimation shock in the jets is expected due to the wind impact. Their distribution along the jet path is obtained assuming local acceleration at the recollimation shock, and cooling via adiabatic, synchrotron, and inverse Compton processes. The synchrotron and inverse Compton emission is calculated taking into account synchrotron self-absorption within the jet, free-free absorption with the stellar wind, and absorption by stellar photons via pair production. Results. The spectrum is totally dominated by the jet over the counter-jet due to Doppler boosting. Broadband emission from microwaves to gamma rays is predicted, with radio emission being totally absorbed. This emission is rather concentrated in the regions close to the binary system and features strong orbital modulation at high energies. Asymmetric light curves are obtained owing to the helical trajectory of the jets. Conclusions. The presence of helical shaped jets could be inferred from asymmetries in the light curves, which become noticeable only for large jet Lorentz factors and low magnetic fields. Model parameters could be constrained if accurate phase-resolved light curves from GeV to TeV energies were available. The predictions for the synchrotron and the inverse Compton radiation are quite sensitive of the parameters determining the wind-jet interaction structure.

Relativistic hydrodynamical simulations of the effects of the stellar wind and the orbit on high-mass microquasar jets

“…The simulations done did not take into account that the stellar wind formation can be inhibited in the hemisphere facing the CO, which happens when there is a strong CO accretion X-ray luminosity that ionizes the accelerating stellar wind close to the star (see, e.g., Meyer-Hofmeister et al 2020;Vilhu et al 2021, for Cygs X-1 and Cygs X-3, respectively). As discussed in Molina et al (2019), the wind moving in that hemisphere should be slowed down when forming close to the star and then, beamed towards the CO due to its strong gravitational pull (e.g. El Mellah et al 2019), acquiring a higher velocity once within the CO potential well.…”

“…Analytical and semi-analytical treatments have shown that this influence leads to a helical geometry, which can further enhance instability development in the jet Bosch-Ramon 2013;Bosch-Ramon & Barkov 2016). This influence can also affect the high- energy emission of HMMQ, which are confirmed gammaray sources, as shown by Molina & Bosch-Ramon (2018) and Molina et al (2019). The strength of the wind and the orbit influences on the jet is expected to be directly related to the intercepted wind-to-jet momentum rate ratio: First, the more wind momentum rate is intercepted by the jet, the more inclined the jet becomes away from the star.…”

A dynamical and radiation semi-analytical model of pulsar-star colliding winds along the orbit: Application to LS 5039

“…ation of a semi-analytical hydrodynamical approach to study the combined effect of the stellar wind and orbital motion on the emitter, which is assumed to be one-dimensional (1D) (see Molina & Bosch-Ramon 2018;Molina et al 2019, for a similar model in a microquasar scenario). The paper is structured as follows: the details of the model are given in Sect.…”

“…This behavior is not exclusive of a colliding wind scenario, however, since the jets in a microquasar scenario could be affected by orbital motion in a similar manner (e.g. Bosch-Ramon 2013; Molina & Bosch-Ramon 2018;Molina et al 2019).…”

Effects of radiative losses on the relativistic jets of high-mass microquasars

“…Mirabel & Rodriguez 1999;Gallo et al 2005) at relativistic speeds either from the accretion disc of the compact object through the Blandford-Payne magnetocentrifugal ejection mechanism (Blandford & Payne 1982), or the black hole (BH) magnetosphere through the Blandford-Znajek mechanism (Blandford & Znajek 1977). Jets are of interest as integral parts of the astrophysical objects harboring them, but also because their impressive stability due to collimation allows them to extend orders of magnitude farther than their injection scale (Migliori et al 2017;, offering a very powerful way to study their environment or their contribution to observed thermal (radio), but also (nonthermal) emissions (Malzac 2014;Zdziarski et al 2014;Rodriguez et al 2015;Molina et al 2019;Albert et al 2021;Motta et al 2021).…”