A Reemerging Bright Soft X-Ray State of the Changing-look Active Galactic Nucleus 1ES 1927+654: A Multiwavelength View
Cenko, S. Bradley; Meyer, Eileen; Lusso, Elisabeta; Acosta-Pulido, J. A.; Bianchi, Stefano; La Franca, Fabio; Laha, Sibasish; Gabányi, Krisztina Éva; Hammerstein, Erica; Behar, Ehud; Nicholl, Matt; Gallo, Luigi C.; Begelman, Mitchell C.; Panessa, Francesca; O'Connor, Brendan; Yang, Xiaolong; Ricci, Federica; Rakshit, Suvendu; Longinotti, Anna Lia; Ghosh, Ritesh; Oates, Samantha; Roychowdhury, Agniva; Scepi, Nicolas; Chattopadhyay, Sabyasachi; Pandey, Shivangi; González, Josefa Becerra; Jose, Jincen
United States, China, Spain, India, Israel, Canada, Italy, United Kingdom, Mexico, Hungary, South Africa
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 (L radio/L X-ray ~ 10-5), however, is still within the expected range for radio-quiet AGNs, and further follow-up radio observations are currently being undertaken.