X-ray timing of active galactic nuclei (AGN) provides a unique probe of gas accretion onto supermassive black holes (SMBHs). Quasi-periodic oscillations (QPOs), which trace gas dynamics in the strongly curved spacetime around SMBHs, are rare in AGN. These signals often are analogs of high-frequency QPOs occasionally seen in some black-hole X-ray binaries, and their scarcity in AGN can partly be attributed to the low frequencies expected for typical SMBH masses. Intriguingly, robust X-ray QPO detections in SMBH systems have so far been reported only in narrow-line Seyfert 1 galaxies (NLS1s) and tidal disruption events (TDEs). Here we report the discovery of a QPO candidate during the 2018 outburst of the changing-look AGN (CL-AGN) NGC 1566. Numerical simulations indicate that the disk epicyclic oscillations responsible for high-frequency QPOs are damped by magnetohydrodynamic turbulence unless the accretion flow is misaligned and/or eccentric. In TDEs, the stellar debris stream is naturally misaligned with the SMBH spin, while NLS1s may host misaligned disks due to their youth. Motivated by the QPO candidate in NGC 1566, we propose that CL-AGN accretion is also misaligned -- potentially fueled by captured, free-falling broad-line region clouds. This model naturally explains why CL-AGN transition timescales are much shorter than the standard disk viscous timescale. This picture can be tested by searching for QPOs or quasi-periodic eruptions in other CL-AGN.
Measurement of the mass-changing, charge-changing and production cross sections of $^{11}$C, $^{11}$B and $^{10}$B nuclei in $^{12}$C+p interactions at 13.5 GeV/c per nucleon
A systematic study of the condensation of the corona and the application for $Γ_{\rm 2-10keV}-L_{\rm bol}/L_{\rm Edd}$ correlation in luminous active galactic nuclei
Multi-wavelength properties of changing-state active galactic nuclei: I. the evolution of soft excess and X-ray continuum
Universidad Diego Portales（迭戈·波特莱斯大学）；SRM University-AP（SRM大学安得拉邦校区）；University of Geneva（日内瓦大学）；Peking University（北京大学）；INAF-Osservatorio Astronomico di Roma（意大利国家天文台罗马天文台）；Tel Aviv University（特拉维夫大学）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；Excellence Cluster ORIGINS（ORIGINS卓越集群）；Universidad de Tarapacá（塔拉帕卡大学）；Durham University（杜伦大学）；Eureka Scientific（尤里卡科学公司）；Space Science Institute（太空科学研究所）；Liège Université（列日大学）；Universiteit Gent（根特大学）；National Tsing Hua University（国立清华大学）
A Fit to the Galactic Cosmic Ray Hydrogen and Helium Spectra at Voyager 1 at Low Energies and Earth Based Measurements at Much Higher Energies with Identical Rigidity Independent Source Spectra for the Hydrogen and Helium Nuclei
