Observational Evidence of an Internal Shock Collision in the Relativistic Jet of the Nearby Radio Galaxy 3C 111
Abstract
We report 10 epochs of 22 GHz East Asia To Italy: Nearly Global VLBI (EATING VLBI) observations of the nearby radio galaxy 3C~111 obtained from 2020 to 2023. Combined with VLBA data at 15 and 43 GHz, these observations yield a 64-epoch, multi-frequency sequence of high-resolution radio images. We used high-resolution Bayesian Stokes~I imaging and Gaussian component modeling to derive light curves and knot kinematics. We find evidence that a faster, later-emitted knot catches up with a slower, earlier knot at a deprojected distance of about 10 pc from the central engine. The knot component responsible for this interaction propagated at relativistic speed and exhibited a rise-and-decay evolution over approximately six months. The Stokes~I flux evolution supports the internal shock interpretation, while archival polarization images reveal a temporary increase in fractional linear polarization in the interaction region near the Stokes~I flux maximum. The timing of the 2021 GeV flare suggests that this earlier high-energy event is more naturally associated with activity near the core. These results provide direct evidence for an internal shock in an active galactic nucleus jet and support a hybrid picture in which internal and standing shocks coexist in relativistic jets and may play different roles in their variability.
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BibTeX
@misc{kawamura2026observational,
title = {{Observational Evidence of an Internal Shock Collision in the Relativistic Jet of the Nearby Radio Galaxy 3C 111}},
author = {Kenzo Kawamura and Motoki Kino and Mareki Honma and Kazuhiro Hada and Paul Tiede and Evgeniya Kravchenko and Marcello Giroletti and Rocco Lico and Kazunori Akiyama and Mieko Takamura and Filippo D'Ammando and Monica Orienti and Gabriele Giovannini and Fumie Tazaki and Bong Won Sohn and Salvatore Buttaccio and Lang Cui and Giuseppe Maccaferri and Andrea Melis and Alexey Melnikov and Carlo Migoni and Matteo Stagni and Kiyoaki Wajima and Takeshi Sakai},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.23410},
eprint = {2609.23410},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.23410},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Observational Evidence of an Internal Shock Collision in the Relativistic Jet of the Nearby Radio Galaxy 3C 111
AU - Kenzo Kawamura
AU - Motoki Kino
AU - Mareki Honma
AU - Kazuhiro Hada
AU - Paul Tiede
AU - Evgeniya Kravchenko
AU - Marcello Giroletti
AU - Rocco Lico
AU - Kazunori Akiyama
AU - Mieko Takamura
AU - Filippo D'Ammando
AU - Monica Orienti
AU - Gabriele Giovannini
AU - Fumie Tazaki
AU - Bong Won Sohn
AU - Salvatore Buttaccio
AU - Lang Cui
AU - Giuseppe Maccaferri
AU - Andrea Melis
AU - Alexey Melnikov
AU - Carlo Migoni
AU - Matteo Stagni
AU - Kiyoaki Wajima
AU - Takeshi Sakai
PY - 2026
DA - 2026/09/20
PB - arXiv
DO - 10.48550/arxiv.2609.23410
UR - https://arxiv.org/abs/2609.23410
AB - We report 10 epochs of 22 GHz East Asia To Italy: Nearly Global VLBI (EATING VLBI) observations of the nearby radio galaxy 3C~111 obtained from 2020 to 2023. Combined with VLBA data at 15 and 43 GHz, these observations yield a 64-epoch, multi-frequency sequence of high-resolution radio images. We used high-resolution Bayesian Stokes~I imaging and Gaussian component modeling to derive light curves and knot kinematics. We find evidence that a faster, later-emitted knot catches up with a slower, earlier knot at a deprojected distance of about 10 pc from the central engine. The knot component responsible for this interaction propagated at relativistic speed and exhibited a rise-and-decay evolution over approximately six months. The Stokes~I flux evolution supports the internal shock interpretation, while archival polarization images reveal a temporary increase in fractional linear polarization in the interaction region near the Stokes~I flux maximum. The timing of the 2021 GeV flare suggests that this earlier high-energy event is more naturally associated with activity near the core. These results provide direct evidence for an internal shock in an active galactic nucleus jet and support a hybrid picture in which internal and standing shocks coexist in relativistic jets and may play different roles in their variability.
ER -