Sub-Parsec Acceleration and Collimation of NGC 4261's Twin Jets
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| Autores principales: | , , , , , , , , |
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| Formato: | Preprint |
| Publicado: |
2025
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| author | Yan, Xi Cui, Lang Hada, Kazuhiro Frey, Sandor Lu, Ru-sen Chen, Liang Xu, Wancheng Fariyanto, Elika P. Ho, Luis C. |
| author_facet | Yan, Xi Cui, Lang Hada, Kazuhiro Frey, Sandor Lu, Ru-sen Chen, Liang Xu, Wancheng Fariyanto, Elika P. Ho, Luis C. |
| contents | We report the first robust evidence for a co-spatial sub-parsec acceleration and collimation zone (ACZ) in the twin jets of the nearby low-luminosity active galactic nucleus (LLAGN) NGC 4261. This result is derived from multifrequency Very Long Baseline Array imaging, combined with the frequency-dependent properties of the radio core (core shift and core size) and jet kinematics determined from the jet-to-counterjet brightness ratio. By applying multiple analysis methods and incorporating results from the literature, we identify a parabolic-to-conical structural transition in both the jet and counterjet, with the transition occurring at $(1.23\pm0.24)$ pc or $(8.1\pm1.6)\times10^3 R_{\rm s}$ (Schwarzschild radii) for the jet and $(0.97\pm0.29)$ pc or $(6.4\pm1.9)\times10^3 R_{\rm s}$ for the counterjet. We also derive the jet velocity field at distances of $\sim (10^3-2\times10^4) R_{\rm s}$. While local kinematic variations are present, the jet shows an overall acceleration to relativistic speeds from $\sim 10^3$ to $\sim8\times10^3 R_{\rm s}$, with a maximum Lorentz factor of $Γ_{\rm max} \approx 2.6$. Beyond this region, the jet gradually decelerates to sub-relativistic speeds. These findings support the existence of a sub-parsec-scale ($\lesssim 1.5$ pc) ACZ in NGC 4261, where the jet is accelerated via magnetic-to-kinetic energy conversion while being confined by external pressure. A brief comparison with M 87 suggests that the ACZ in NGC 4261 may represent a scaled-down analogue of that in M 87. These results point towards a potential diversity in jet ACZ properties, emphasizing the importance of extending such studies to a broader AGN population to elucidate the physical mechanisms at play. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_13093 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Sub-Parsec Acceleration and Collimation of NGC 4261's Twin Jets Yan, Xi Cui, Lang Hada, Kazuhiro Frey, Sandor Lu, Ru-sen Chen, Liang Xu, Wancheng Fariyanto, Elika P. Ho, Luis C. Astrophysics of Galaxies High Energy Astrophysical Phenomena We report the first robust evidence for a co-spatial sub-parsec acceleration and collimation zone (ACZ) in the twin jets of the nearby low-luminosity active galactic nucleus (LLAGN) NGC 4261. This result is derived from multifrequency Very Long Baseline Array imaging, combined with the frequency-dependent properties of the radio core (core shift and core size) and jet kinematics determined from the jet-to-counterjet brightness ratio. By applying multiple analysis methods and incorporating results from the literature, we identify a parabolic-to-conical structural transition in both the jet and counterjet, with the transition occurring at $(1.23\pm0.24)$ pc or $(8.1\pm1.6)\times10^3 R_{\rm s}$ (Schwarzschild radii) for the jet and $(0.97\pm0.29)$ pc or $(6.4\pm1.9)\times10^3 R_{\rm s}$ for the counterjet. We also derive the jet velocity field at distances of $\sim (10^3-2\times10^4) R_{\rm s}$. While local kinematic variations are present, the jet shows an overall acceleration to relativistic speeds from $\sim 10^3$ to $\sim8\times10^3 R_{\rm s}$, with a maximum Lorentz factor of $Γ_{\rm max} \approx 2.6$. Beyond this region, the jet gradually decelerates to sub-relativistic speeds. These findings support the existence of a sub-parsec-scale ($\lesssim 1.5$ pc) ACZ in NGC 4261, where the jet is accelerated via magnetic-to-kinetic energy conversion while being confined by external pressure. A brief comparison with M 87 suggests that the ACZ in NGC 4261 may represent a scaled-down analogue of that in M 87. These results point towards a potential diversity in jet ACZ properties, emphasizing the importance of extending such studies to a broader AGN population to elucidate the physical mechanisms at play. |
| title | Sub-Parsec Acceleration and Collimation of NGC 4261's Twin Jets |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2506.13093 |