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

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 $ν<em>{\rm p} = 0.48 \pm 0.03$ GHz and a peak flux density $S</em>{\rm p} = 38.9 \pm 4.7$ 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 $β_{\rm app} \approx 0.64$. The observed brightness temperature $T_b \approx 6.0 \times 10<sup>{11}$ K necessitates a Doppler factor $δ\approx 12$, implying a relativistic jet viewed at $θ\lesssim 5<sup>\circ$. Despite the dramatic radio evolution, the X-ray spectrum remains stable and steep ($Γ\simeq 3.0$), 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.

• The paper demonstrates the emergence of a young, relativistic jet in J1105+1452, marked by a >20-fold increase in radio flux.
• It employs multi-wavelength data and synchrotron self-absorption modeling to derive key jet parameters, including a turnover at 0.48 GHz.
• The findings challenge conventional jet-launching models by showing significant radio changes with minimal X-ray response in high Eddington ratio AGN.

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

Introduction

The study presents a comprehensive multi-wavelength analysis of SDSS J110546.07+145202.4 (hereafter J1105+1452), a narrow-line Seyfert 1 (NLSy1) galaxy that underwent a transition from a radio-quiet to an extremely radio-loud state. This evolution is interpreted as the emergence of a relativistic jet. The authors utilize radio, X-ray, optical, and mid-infrared (MIR) data from numerous surveys and targeted observations spanning several decades, with a particular focus on characterizing the jet physics and its coupling to the accretion flow in a high Eddington ratio AGN.

Long-term Radio Evolution and Jet Emergence

J1105+1452 was historically radio-quiet, with 1.4 GHz flux densities of $\sim1.4$ mJy in the 1990s, consistent with classic NLSy1s typically lacking powerful jets. A dramatic increase by a factor of $\gtrsim$20 in its radio flux density was detected after 2017, persisting at the 30--40 mJy level at GHz frequencies. This enhancement places its current radio-loudness parameter $R_{5\,\mathrm{GHz}} \sim 173$—a shift well into the extremely radio-loud regime, contrasting with a historical value of $\sim 9.6$ derived from archival photometry and FIRST data.

The radio spectral energy distribution (SED) constructed from multi-epoch and multi-frequency data exhibits a pronounced turnover at 0.48 GHz, with a peak flux density $S_p = 38.9 \pm 4.7$ mJy. The suppression at 144 MHz, measured by LoTSS at $1.94 \pm 0.23$ mJy, is incompatible with an unabsorbed power-law and requires a compact, absorbed component. Synchrotron self-absorption (SSA) modeling reproduces the SED and supports a classification as a Megahertz Peaked-Spectrum (MPS) source, implying a young, compact jet. An alternative free-free absorption (FFA) model is physically viable but cannot be distinguished without deeper low-frequency coverage.

Multi-wavelength Constraints

X-ray Properties

Despite the violent radio evolution, X-ray monitoring from 2020 to 2025 (eROSITA, Swift/XRT, and Einstein Probe/FXT) reveals a statistically steady X-ray continuum ($F_{0.5-8.0\,\mathrm{keV}} = 1.79 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$) and persistently steep power-law spectra ($\Gamma \simeq 3.0$). The historical ROSAT detection from 1990 is consistent in flux and slope. No significant changes in flux or photon index correspond to the radio outburst epoch, indicating disk–corona dominance in the X-ray regime and minimal high-energy contribution from the jet. This decoupling is a strong empirical result, sharply distinguishing this event from typical blazar-like variability profiles.

High-energy Gamma-ray Observations

Fermi-LAT analysis (2017–2025) shows no significant $\gtrsim$0-ray emission from J1105+1452, with stringent TS$\gtrsim$1 upper limits. This non-detection is notable given the inferred jet orientation and Doppler factor, and constrains both the compactness of the jet and the available external photon field for efficient inverse Compton scattering.

Optical and MIR Variability

Systematic analysis of Catalina, ASAS-SN, ATLAS, ZTF, Pan-STARRS1, and WISE/NEOWISE data reveals a decade-long optical/MIR fading followed by a gradual rise and stabilization phase. Post-2017, the nucleus is consistently $\gtrsim$2 mag brighter across several optical filters compared to the 2003 SDSS baseline, consistent with a moderate enhancement in nuclear activity. MIR light curves track the optical trends, displaying a fading-then-stabilization pattern and a modest increase coeval with the establishment of the radio-bright phase. The lag and correlated behavior are consistent with dust reverberation scenarios.

Jet Physics: Compactness, Kinematics, and Energetics

Applying SSA-based equipartition arguments, the jet radius is inferred to be $\gtrsim$3 pc, with a corresponding angular scale of $\gtrsim$4 mas. Given the interval between the accretion flow stabilization (optical/MIR) and the onset of GHz radio brightness (VLASS detection), a characteristic expansion velocity $\gtrsim$5 is derived. The observed brightness temperature, $\gtrsim$6 K, significantly exceeds the canonical equipartition limit, supporting a Doppler factor $\gtrsim$7 and a jet inclination $\gtrsim$8. The jet power, estimated via empirical scaling relations and equipartition analysis, falls in the range $\gtrsim$9 erg s$R_{5\,\mathrm{GHz}} \sim 173$0, with uncertainties due to relativistic boosting.

These parameters place J1105+1452 squarely within the young radio source/MPS locus, with physical properties comparable to FSRQs and jetted NLSy1s during early jet evolution phases. The absence of a flat-spectrum core at sub-parsec scales and the modestly superluminal expansion rate further support this interpretation.

Theoretical and Phenomenological Implications

J1105+1452 constitutes a direct observation of a radio changing-state NLSy1 galaxy. The identification of a jet formation event in a high Eddington ratio, low-mass SMBH system is contradictory to canonical models, in which powerful, persistent relativistic jets are typically restricted to low-accretion, high-black-hole-mass systems hosted in ellipticals. The event demonstrates that rapid transitions to relativistic jet-dominated states can occur in systems with previously quiescent radio histories and strong disk emission, indicating a flexibility in jet launching physics beyond simple unification schemes [Urry & Padovani 1995].

The negligible X-ray response indicates the jet emergence is not driven by a global accretion state transition but rather by localized or stochastic conditions in the inner disk or magnetosphere. The absence of a GeV counterpart, despite a small viewing angle and high Doppler factor, suggests either insufficient seed photon density for external Compton processes, internal $R_{5\,\mathrm{GHz}} \sim 173$1-ray absorption, or a currently compact dissipation zone.

Future Prospects

High-resolution VLBI is required to resolve the compactness, measure direct expansion rates, and identify jet components. Future X-ray and $R_{5\,\mathrm{GHz}} \sim 173$2-ray monitoring may detect late-time high-energy emission should the jet structure evolve toward larger scales or more efficient external Compton cooling. Additional low-frequency radio data are necessary to distinguish SSA from FFA and to constrain the jet spectral curvature. This source provides a benchmark for testing models of disk-jet coupling at high Eddington rates and for exploring the duty cycle and recurrence of jet activity in NLSy1s.

Conclusion

J1105+1452 exemplifies the emergence of a relativistic, Doppler-boosted jet in a NLSy1 galaxy transitioning from radio quiet to radio loud on short timescales. Strong claims of radio-brightening by more than one order of magnitude with minimal X-ray or optical response are robustly supported by multi-wavelength data. The inferred physical properties—compact size, high $R_{5\,\mathrm{GHz}} \sim 173$3, large Doppler boosting, and SSA-dominated spectrum—signal a very young, highly beamed jet. These results demand reconsideration of jet-launching paradigms in high-accretion AGN and motivate continued multi-band time-domain studies of changing-state active galaxies (2604.17049).