Evolution of a Relativistic Outflow and X-Ray Corona in the Extreme Changing-look AGN 1ES 1927+654

• Published in: The Astrophysical journal 2022-07, Vol.934 (1), p.35
• Main Authors: Masterson, Megan, Kara, Erin, Ricci, Claudio, García, Javier A., Fabian, Andrew C., Pinto, Ciro, Kosec, Peter, Remillard, Ronald A., Loewenstein, Michael, Trakhtenbrot, Benny, Arcavi, Iair
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Astrophysics; Blackbody; Corona; Deposition; Emission; Emission lines; Emissions; Evolution; High energy astrophysics; Luminosity; Mathematical models; Outflow; Parameters; Seyfert galaxies; Supermassive black holes; X ray spectra; X-ray fluxes; X-ray transient sources; X-rays; XMM (spacecraft)
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac76c0

1ES 1927+654 is a paradigm-defying active galactic nucleus (AGN) and one of the most peculiar X-ray nuclear transients. In early 2018, this well-known AGN underwent a changing-look event, in which broad optical emission lines appeared and the optical flux increased. Yet, by 2018 July, the X-ray flux had dropped by over two orders of magnitude, indicating a dramatic change in the inner accretion flow. With three years of observations with NICER, XMM-Newton, and NuSTAR, we present the X-ray evolution of 1ES 1927+654, which can be broken down into three phases: (1) an early super-Eddington phase with rapid variability in X-ray luminosity and spectral parameters, (2) a stable super-Eddington phase at the peak X-ray luminosity, and (3) a steady decline back to the pre-outburst luminosity and spectral parameters. For the first time, we witnessed the formation of the X-ray corona, as the X-ray spectrum transitioned from thermally dominated to primarily Comptonized. We also track the evolution of the prominent, broad 1 keV feature in the early X-ray spectra and show that this feature can be modeled with blueshifted reflection ( z = −0.33) from a single-temperature blackbody irradiating spectrum using xillverTDE , a new flavor of the xillver models. Thus, we propose that the 1 keV feature could arise from reflected emission off the base of an optically thick outflow from a geometrically thick, super-Eddington inner accretion flow, connecting the inner accretion flow with outflows launched during extreme accretion events (e.g., tidal disruption events). Lastly, we compare 1ES 1927+654 to other nuclear transients and discuss applications of xillverTDE to super-Eddington accretors.