Title：Beating the Viscous Clock: Disk Instabilities Behind Changing-Look AGN

Speaker:Agnieszka Janiuk (Center for Theoretical Physics, Polish Acadecmy of Sciences)

Time：3:00 pm Oct.16th (Thursday)

Tencent Meeting：46822606747 password: 6360

Location: Lecture Hall, 3rd floor

Abstract：

Changing-look active galactic nuclei (CL AGN) exhibit abrupt transitions in continuum luminosity, broad-line emission, and apparent obscuration. Large time-domain and spectroscopic surveys have now established sizable samples that include both turn-on and turn-off events on rest-frame timescales of ≲ decade, and an emerging subset of recurrent CL episodes. Coordinated mid-infrared variability that lags the optical/UV in many objects points to torus reverberation, favoring intrinsic changes in the accretion flow over variable line-of-sight extinction for the bulk of dramatic optical CL cases. We model CL behavior as the time-dependent evolution of an accretion flow that can depart from the standard thin-disc regime: a radiation-pressure-unstable disc coupled to a hot corona, and/or a magnetically elevated, wind-torqued disc that shortens inflow times and enables rapid state changes, including possible transitions to an inner optically thin, advection-dominated flow. Using a vertically integrated, time-dependent disc–corona framework, we explore how large-scale magnetic flux, wind torques, and coronal heating regulate the amplitudes and timescales of CL transitions. We outline multi-wavelength diagnostics—optical–MIR lags, contemporaneous X-ray/UV spectral evolution, and velocity-resolved reverberation mapping of the BLR—to distinguish intrinsic accretion variability from obscuration-driven scenarios and to map the parameter space (accretion rate, magnetic flux, wind efficiency) that reproduces observed CL cycles.

For context, we briefly contrast these year-scale changing-look transitions with quasi-periodic X-ray eruptions (QPEs)—hour–day soft-X-ray flares likely tied to episodic inner-disc feeding (e.g., post-TDE debris or star–disk encounters)—which probe similar inner-flow physics but are observationally distinct from optical CL events.

CV：

Prof. Agnieszka Janiuk – Polish astrophysicist, Professor at the Center for Theoretical Physics of the Polish Academy of Sciences. Member of the National Council for Particle Astrophysics,  Polish Astronomical Society, and the Polish Society of Relativity. Completed PhD at the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences in Warsaw, in 2003.Worked as a postdoctoral fellow at the University of Nevada, Las Vegas. Later as tenure-track at the Nicolaus Copernicus Astronomical Center and simultaneously (2010-2011) as an assistant professor at the Center for Theoretical Physics of the Polish Academy of Sciences. Since November 2011, he has been appointed a professor at the Centre for Theoretical Physics of the Polish Academy of Sciences Received habilitation (tenure) in physical sciences in astronomy in 2011, and the title of professor in the field of exact and natural sciences from the President of the Republic of Poland in January 2021. Author of over 180 scientific publications. Her research interests include: astrophysics of accretion disks in binary systems, black holes in the Milky Way, active galactic nuclei and quasars, and the origin of gamma-ray bursts.