Abstract:
1ES1927+654 is a nearby active galactic nucleus (AGN) that has shown an enigmatic outburst in optical/UV
followed by X-rays, exhibiting strange variability patterns at timescales of months to years. Here we report the
unusual X-ray, UV, and radio variability of the source in its postflare state (2022 January–2023 May). First, we
detect an increase in the soft X-ray (0.3–2 keV) flux from 2022 May to 2023 May by almost a factor of 5, which we
call the bright soft state. The hard X-ray 2–10 keV flux increased by a factor of 2, while the UV flux density did not
show any significant changes ( 30%) in the same period. The integrated energy pumped into the soft and hard
X-rays during this period of 11 months is ∼3.57 × 1050 erg and 5.9 × 1049 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 supermassive black
hole, the SE-emitting region must be receiving the majority of this energy. In addition, the source does not follow the
typical disk–corona relation found in AGNs, neither in the initial flare (from 2017 to 2019) nor in the current bright
soft state (2022–2023). We found that the core (<1 pc) radio emission at 5 GHz gradually increased until 2022
March, but showed a dip in 2022 August. The Güdel–Benz relation (Lradio/LX-ray ∼ 10−5
), however, is still within
the expected range for radio-quiet AGNs, and further follow-up radio observations are currently being undertaken.
