Multi-wavelength observations of a jet launch in real time from the post-changing-look Active Galaxy 1ES 1927+654

Abstract: We present results from a high cadence multi-wavelength observational campaign of the enigmatic changing look AGN 1ES 1927+654 from May 2022- April 2024, coincident with an unprecedented radio flare (an increase in flux by a factor of $\sim 60$ over a few months) and the emergence of a spatially resolved jet at $0.1-0.3$ pc scales (Meyer et al. 2024). Companion work has also detected a recurrent quasi-periodic oscillation (QPO) in the $2-10$ keV band with an increasing frequency ($1-2$ mHz) over the same period (Masterson et al., 2025). During this time, the soft X-rays ($0.3-2$ keV) monotonically increased by a factor of $\sim 8$, while the UV emission remained near-steady with $<30\%$ variation and the $2-10$ keV flux showed variation by a factor $\lesssim 2$. The weak variation of the $2-10$ keV X-ray emission and the stability of the UV emission suggest that the magnetic energy density and accretion rate are relatively unchanged, and that the jet could be launched due to a reconfiguration of the magnetic field (toroidal to poloidal) close to the black hole. Advecting poloidal flux onto the event horizon would trigger the Blandford-Znajek (BZ) mechanism, leading to the onset of the jet. The concurrent softening of the coronal slope (from $\Gamma= 2.70\pm 0.04$ to $\Gamma=3.27\pm 0.04$), the appearance of a QPO, and low coronal temperature ($kT_{e}=8_{-3}^{+8}$ keV) during the radio outburst suggest that the poloidal field reconfiguration can significantly impact coronal properties and thus influence jet dynamics. These extraordinary findings in real time are crucial for coronal and jet plasma studies, particularly as our results are independent of coronal geometry.

• The paper reveals that AGN 1ES 1927+654 experienced a jet launch marked by a 60-fold increase in radio flux and mildly relativistic jet speeds.
• The study employs high-resolution VLBA, XMM-Newton, and NuSTAR observations to correlate radio flares, X-ray softening, and quasi-periodic oscillations with jet formation.
• The findings imply that magnetic field reconfiguration via the Blandford-Znajek mechanism drives jet activity, while the accretion disk's UV emissions remain stable.

Multi-wavelength Observations of Jet Launch in AGN 1ES 1927+654

The paper presents a comprehensive multi-wavelength study of the changing-look active galactic nucleus (CL-AGN) 1ES 1927+654, focusing on a unique period of jet formation and evolution. The study spans from May 2022 to April 2024 and entails detailed observations during an unprecedented radio flare event alongside the emergence of a spatially resolved jet at parsec scales. The radio flux increased by a factor of 60 over a short time, highlighting a significant phase in this AGN's dynamic activity.

Summary of Observational Findings

1. Radio Observations and Jet Formation: An extensive radio monitoring campaign uncovered a dramatic increase in radio flux at GHz frequencies, with spatially resolved jets detected at $0.1-0.3$ pc scales. The observed speed of the jet components is mildly relativistic, around $0.2c$. These findings were facilitated by high-angular resolution observations using VLBA, capturing jet evolution in real time.
2. X-ray Observations: Simultaneous X-ray observations with XMM-Newton and NuSTAR indicate a significant increase in the soft X-ray flux by a factor of approximately 8, contrasting with mild variations in the 2-10 keV range. This softening of the X-ray spectrum coincided with the jet's advent, characterized by a spectral slope progression from $\Gamma=2.70\pm 0.04$ to $\Gamma=3.27\pm 0.04$.
3. UV and Optical Stability: Despite the dramatic changes observed in radio and X-ray regimes, UV emissions remain notably stable, exhibiting variations under 30%. This stability suggests the accretion disk's magnetic energy density and accretion rate have not undergone significant changes during the observation period.
4. QPO Detection: Accompanying the multi-wavelength observations is the detection of a recurring quasi-periodic oscillation (QPO) in the 2-10 keV band, with an increasing frequency from $1$ to $2$ mHz. This feature provides insights into coherent processes occurring at close proximities to the black hole, potentially linked to jet launching mechanisms.

Implications and Theoretical Context

The study's findings underline the relevance of the Blandford-Znajek mechanism in explaining jet formation in 1ES 1927+654. The configuration of magnetic fields, transitioning from toroidal to poloidal, seems crucial for triggering jet emissions by tapping energy from the black hole's rotational dynamics. This process is independent of coronal geometry and spatial orientation, though intricacies in plasma dynamics—such as coronal temperature reductions to $kT_{e}=8_{-3}^{+8}$ keV—underscore the need for further exploration into coronal evolution's role in modulating jet activities and QPO appearances.

The research also dovetails ongoing inquiries into AGN's broad emission regions and the factors underpinning changing-look phenomena. Delving into AGN jet dynamics contributes to a broader understanding of relativistic jets generally preserved across varying redshifts and diverse galactic environments. Monitoring the temporal dynamics of such systems provides essential data for advancing models of jet mechanisms within the AGN cosmological framework.

Conclusion

This study of 1ES 1927+654 invokes numerous considerations for future theoretical and observational work. It emphasizes the necessity for high cadence, multi-wavelength observational campaigns when exploring the nuanced interplay of jets, accretion phenomena, and coronal activities. Furthermore, it sets a precedent for assessing changes in AGN emissions under comprehensive frameworks that account for both stable disk emissions and robust, extragalactic outflow properties. These insights enrich the developing landscape of jet physics and AGN evolution, promising deeper integration into broader astrophysical contexts.