A re-emerging bright soft-X-ray state of the changing-look Active Galactic Nucleus 1ES~1927+654: a multi-wavelength view

TL;DR

This study reports a significant brightening in soft X-ray emission of the changing-look AGN 1ES 1927+654, revealing a new soft state with unusual energetics and variability patterns across multiple wavelengths, challenging standard accretion models.

Contribution

It provides the first detailed multi-wavelength analysis of the re-emerging soft X-ray state in 1ES 1927+654, highlighting deviations from typical AGN disc-corona relations and energy distribution.

Findings

Soft X-ray flux increased by a factor of five from May 2022 to May 2023.

The soft excess energy output exceeds that of UV and hard X-ray emissions.

Radio core emission showed a gradual increase with a dip in August 2022.

Abstract

1ES1927+654 is a nearby active galactic nucleus that has shown an enigmatic outburst in optical/UV followed by X-rays, exhibiting strange variability patterns at timescales of months-years. Here we report the unusual X-ray, UV, and radio variability of the source in its post-flare state (Jan 2022- May 2023). Firstly, we detect an increase in the soft X-ray (0.3-2 keV) flux from May 2022- May 2023 by almost a factor of five, which we call the bright-soft-state. The hard X-ray 2-10 keV flux increased by a factor of two, while the UV flux density did not show any significant changes ($\le 30\%$) in the same period. The integrated energy pumped into the soft and hard X-ray during this period of eleven months is $\sim 3.57\times 10^{50}$ erg and $5.9\times 10^{49}$ erg, respectively. From the energetics, it is evident that whatever is producing the soft excess (SE) is pumping out more energy than either the UV or hard X-ray source. Since the energy source presumably is ultimately the accretion of matter onto the SMBH, the SE emitting region must be receiving the majority of this energy. In addition, the source does not follow the typical disc-corona relation found in AGNs, neither in the initial flare (in 2017-2019) nor in the current bright soft state (2022-2023). We found that the core (<1 pc) radio emission at 5 GHz gradually increased till March 2022 but showed a dip in August 2022. The G\"udel Benz relation ($L_{\rm radio}/L_{\rm X-ray}\sim 10^{-5}$), however, is still within the expected range for radio-quiet AGN and further follow-up radio observations are currently being undertaken.