Effects of precession versus instabilities on the jets of GRS 1758–258

Abstract

Aims. The prototypical microquasar GRS 1758–258 exhibits large-scale morphological changes in radio maps over time which have been attributed to the rise of instabilities. Here, we investigate whether these effects could be attributed to jet precession instead. Methods. We used new and archival radio maps to fit a kinematic jet precession model. The value of the parameters thus obtained were analysed in order to get constraints on the physical properties of the GRS 1758–258 system. Their consistency with different theories of the origins for the jet precession, such as Lense–Thirring effect and tidal torques induced by the secondary star, has previously been studied. Alternatively, we also assessed the possibility that observations are compatible with eventual jet instabilities. Results. The new radio data presented here confirm that the large-scale radio morphology of GRS 1758–258 is changing over time. Our study shows that the 18.48 day period could plausibly be ascribed to precession, thus implying a reinterpretation of assumptions made for the orbital period to date. However, the observed structural changes in radio jets cannot be easily attributed to jet precession according to our analysis. In contrast, the growth of instabilities certainly appears to be a more realistic explanation of these effects.