A Delayed Radio Flare Traces Kinetic Energy Injection in the SMBHB Candidate SDSS~J143016.05+230344.4

A Delayed Radio Flare Traces Kinetic Energy Injection in the SMBHB Candidate SDSS~J143016.05+230344.4
Tao An, Ailing Wang, Yingkang Zhang, Lei Yang, Xinwen Shu, Fabao Zhang, Ning Jiang, Tinggui Wang, Huan Yang, Zhen Pan, Liming Dou, Zhijun Xu, Zhenya Zheng, Ruqiu Lin, Xiaofeng Li
arXiv:2603.07161v2 Announce Type: replace
Abstract: SDSS~J143016.05+230344.4 ($z=0.08105$) has been proposed as a candidate pre-coalescence supermassive black hole binary and shows remarkable multiwavelength variability. Its radio evolution provides a direct probe of the compact emitting region and of the physical origin of the late-time activity. We aim to localize the variable radio emission, characterize its spectral evolution, and constrain whether the radio brightening is produced by a newly emerging compact component, external absorption, or dissipation in a structured circumnuclear environment. At all epochs, the radio emission is dominated by a single unresolved milliarcsecond core with $T_{rm B} gtrsim 10^{7}$ K, constraining the variable emission to $lesssim 0.3$ pc. The broadband spectra require two synchrotron self-absorbed components: a persistent low-frequency component with $nu_{rm p,steady} approx 0.74$ GHz and $S_{rm p,steady} approx 1.22$ mJy, and a flare component whose turnover evolves from $(6.35 {rm GHz}, 0.18 {rm mJy})$ in 2022 February-May to $(8.61 {rm GHz}, 0.38 {rm mJy})$ in 2022 December, and then to $(5.83 {rm GHz}, 0.25 {rm mJy})$ in 2023 March-April. The flare contribution at 15 GHz reaches $sim 80%$ and matches the near-epoch VLBI recovery fraction, showing that the high-frequency brightening arises from a newly formed compact synchrotron component. A second brightening of the 15.2 GHz VLBI core is detected between 2023 September and 2024 February, while the source remains unresolved. Equipartition scalings imply characteristic radii of $sim 5 times 10^{-4}$ pc for the flare and $sim 9 times 10^{-3}$ pc for the steady component, and indicate a steep inner circumnuclear density profile, $n propto R^{-1.7}$. The delayed radio flare is best explained by dissipation in an outflow or jet-base disturbance propagating through a structured circumnuclear medium.arXiv:2603.07161v2 Announce Type: replace
Abstract: SDSS~J143016.05+230344.4 ($z=0.08105$) has been proposed as a candidate pre-coalescence supermassive black hole binary and shows remarkable multiwavelength variability. Its radio evolution provides a direct probe of the compact emitting region and of the physical origin of the late-time activity. We aim to localize the variable radio emission, characterize its spectral evolution, and constrain whether the radio brightening is produced by a newly emerging compact component, external absorption, or dissipation in a structured circumnuclear environment. At all epochs, the radio emission is dominated by a single unresolved milliarcsecond core with $T_{rm B} gtrsim 10^{7}$ K, constraining the variable emission to $lesssim 0.3$ pc. The broadband spectra require two synchrotron self-absorbed components: a persistent low-frequency component with $nu_{rm p,steady} approx 0.74$ GHz and $S_{rm p,steady} approx 1.22$ mJy, and a flare component whose turnover evolves from $(6.35 {rm GHz}, 0.18 {rm mJy})$ in 2022 February-May to $(8.61 {rm GHz}, 0.38 {rm mJy})$ in 2022 December, and then to $(5.83 {rm GHz}, 0.25 {rm mJy})$ in 2023 March-April. The flare contribution at 15 GHz reaches $sim 80%$ and matches the near-epoch VLBI recovery fraction, showing that the high-frequency brightening arises from a newly formed compact synchrotron component. A second brightening of the 15.2 GHz VLBI core is detected between 2023 September and 2024 February, while the source remains unresolved. Equipartition scalings imply characteristic radii of $sim 5 times 10^{-4}$ pc for the flare and $sim 9 times 10^{-3}$ pc for the steady component, and indicate a steep inner circumnuclear density profile, $n propto R^{-1.7}$. The delayed radio flare is best explained by dissipation in an outflow or jet-base disturbance propagating through a structured circumnuclear medium.