Investigating the Jet Width Profile of CTA 102 with Very Long Baseline Interferometry at Parsec Scales

TL;DR

This study uses multi-frequency VLBA observations of CTA 102 to analyze its jet width profile, finding a quasi-parabolic shape without a clear transition to conical form, and revealing oscillatory features suggesting complex physical influences.

Contribution

It provides detailed jet width measurements of CTA 102 across multiple frequencies, challenging the assumption that Bondi radius alone determines jet transition points.

Findings

Jet exhibits a quasi-parabolic shape with index ~0.69

No clear transition to conical structure around Bondi radius

Oscillatory features indicate additional physical processes influence jet collimation

Abstract

Active Galactic Nucleus 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 multi-frequency VLBA images of CTA 102 at 2, 5, and 8 (single epoch), and 15, 22 and 43 GHz (stacked). The jet width profile was modeled with a single power law $W_{jet}\propto r^{\epsilon}$ yielding a power-law index of $\epsilon=0.69\pm0.02$, 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.