Investigating the jet width profile of CTA 102 with very long baseline interferometry at parsec scales

ABSTRACT Active galactic nucleus (AGN) jets have long be thought to exhibit a conical jet shape, but recently, several jets were found to have a transition from parabolic to conical structure. As more sources are investigated, this collimation profile appears to represent a common paradigm. Previous works suggest that the Bondi radius may serve as an indicator of the transition location, although discrepancies have been observed in some sources. To explore this further, we selected CTA 102 for which existing literature presents mixed evidence regarding the presence of a jet geometry break. We investigated the jet width profile of CTA 102 to study the possible transition changes in the jet, thereby improving the understanding of connection between Bondi radius and jet transition. We used multifrequency Very Large Baseline Array (VLBA) images of CTA 102 at 2, 5, and 8 (single epoch), and 15, 22, and 43 GHz (stacked). The jet width profile was modelled with a single power law $W_{\rm {jet}} \propto r^{\epsilon }$ yielding a power-law index of $\epsilon = 0.69\pm 0.02$, indicative of a quasi-parabolic geometry with no clear transition to a conical regime. The absence of discernible structural break around the Bondi radius implies that the physical conditions associated with the radius alone are insufficient to explain the jet collimation behaviour. On the other hand, we observe oscillatory features in the jet width profile, suggesting the influence of additional physical processes beyond gravitational confinement. These findings contribute to a more nuanced understanding of jet collimation in AGN and highlight the complexity of jet–environment interactions.