A Radio Changing-state Jet in the Narrow-line Seyfert 1 Galaxy J1105+1452

TL;DR

This paper reports the discovery of a transition from radio-quiet to radio-loud in the NLSy1 galaxy J1105+1452, revealing the birth of a relativistic jet at high Eddington ratios.

Contribution

It presents the first detailed radio spectral and physical modeling of a changing-state NLSy1 galaxy, linking radio evolution to jet formation.

Findings

J1105+1452 evolved from radio-quiet to radio-loud after 2017.

Radio spectrum indicates a young, compact jet with a turnover frequency of 0.48 GHz.

Doppler boosting suggests a relativistic jet viewed at a small angle.

Abstract

We report the discovery of a radio-quiet to radio-loud transition in the narrow-line Seyfert 1 galaxy J1105+1452. The source has undergone a long-term evolution from a radio-quiet state in the 1990s to a persistently radio-bright state after 2017. Post-2017 flux densities in the $0.8$-$7$ GHz range cluster between $32$ and $43$ mJy, whereas the $144$ MHz flux density is only $1.94 \pm 0.23$ mJy. This indicates strong low-frequency suppression from a compact, absorbed component. Modeling the radio spectral energy distribution with a synchrotron self-absorption model yields a turnover frequency $\nu_{\rm p} = 0.48 \pm 0.03$ GHz and a peak flux density $S_{\rm p} = 38.9 \pm 4.7$ mJy. These parameters classify J1105+1452 as a megahertz peaked-spectrum source, consistent with the new episode of an early-stage compact jet. Under the assumption of equipartition, we derive an intrinsic physical radius $R \sim 0.68$ pc and an average apparent expansion velocity $\beta_{\rm app} \approx 0.64$. The observed brightness temperature $T_b \approx 6.0 \times 10^{11}$ K necessitates a Doppler factor $\delta \approx 12$, implying a relativistic jet viewed at $\theta \lesssim 5^\circ$. Despite the dramatic radio evolution, the X-ray spectrum remains stable and steep ($\Gamma \simeq 3.0$), suggesting that the X-ray emission remains dominated by the disk-corona, while the radio band has become jet-dominated. Our results identify J1105+1452 as a rare radio changing-state NLSy1, providing a unique laboratory for studying the birth and early evolution of relativistic jets at high Eddington ratios.