DOI

https://doi.org/10.48717/2w0k-1j64

Project

RY013

Title

e-EVN: RY013A

Abstract

Cygnus X-3 (Cyg X-3), a high-mass X-ray binary, is notable for its very short orbital period of ~5 hours and for its north–south jet, which shows significant curvature variation on timescales of (1–2) days. Notably, the source has been undergoing giant radio flares since 2026 January 10, reaching flux densities as high as ↓ 22 Jy at 5 GHz. Motivated by this, we propose three-epoch fast Target of Opportunity (ToO) observations with e-EVN at 5 GHz, for a total observing time of 20 hours (5+5+10 hours). Using these observations, we aim to investigate the physical origin of the jet bending, distinguishing between deflection by the stellar wind associated with the orbital motion of the Wolf–Rayet companion and jet precession driven by spin–orbit misalignment in the accretion disk. If the jet bending is induced by the stellar wind, we expect all epochs (5 hours or 10 hours in duration) to reveal a recurring pattern of jet position angle (PA) variation with a characteristic period of ~5 hours. In contrast, if the jet curvature is dominated by jet precession, the PA evolution patterns are expected to di!er among the epochs. In this case, our observations will enable us to characterize jet precession, if present, in unprecedented detail on both minute and hour timescales.