Changing-look active galactic nuclei (CL-AGNs) are a unique class of AGNs that exhibit rapid and dramatic transitions in their spectra, including the appearance or disappearance of broad emission lines. In this study, we analyze a sample of 26 CL-AGNs using spectroscopic data, focusing on the relationships between their variability timescales, Eddington ratios, black hole masses, and broad-line region (BLR) properties. Our results show an inverse correlation between the Eddington ratio and the timescale of changes, indicating that AGNs with higher accretion rates undergo faster transitions. Additionally, we find that the full width at half maximum (FWHM) of the BLR emission lines correlates positively with both black hole mass and Eddington ratio, suggesting stronger gravitational forces and radiation pressure drive faster gas velocities in the BLR. The flux received by the BLR is also positively correlated with the Eddington ratio, emphasizing the close connection between the accretion disk and the BLR. We discuss several models, including accretion disk instabilities, obscuration, and disk winds, to explain these transitions. While accretion rate changes likely play a significant role, the exact mechanisms behind the rapid variability remain debated. Our findings underscore the importance of both the black hole mass and accretion dynamics in shaping the spectral properties and variability of CL-AGNs, contributing to the broader understanding of AGN evolution and the complex interaction between the accretion disk and BLR.

Liu Zhongshu. Research on Changing-Look Events in Active Galactic Nuclei. The Frontiers of Society, Science and Technology (2024), Vol. 6, Issue 11: 80-85. https://doi.org/10.25236/FSST.2024.061114.

[1] Urry, C. M., & Padovani, P. 1995. Unified Schemes for Radio-Loud Active Galactic Nuclei. *Pub. Astron. Soc. Pac.*, 107, 803-845.

[2] MacLeod, C. L., Green, P. J., Anderson, S. F., et al. 2019. Systematic Identification of Changing-look Quasars in SDSS. *Astrophys. J.*, 874(1), 8.

[3] Ricci, C., Koss, M. J., Ueda, Y., et al. 2022. X-ray Variability in Changing-look AGNs. *Astrophys. J.*, 931(1), 56.

[4] Noda, H., & Done, C. 2018. A Magnetic Driving Mechanism for Disk Wind and Corona in Active Galactic Nuclei. *MNRAS*, 480(3), 3898-3911.

[5] Stern, D., LaMassa, S., Moran, E. C., et al. 2018. The Discovery of a Changing-look Quasar at z = 0.32. *Astrophys. J.*, 864(1), 27.

[6] Ruan, J. J., Anderson, S. F., Eracleous, M., Green, P. J., & Morganson, E. 2019. A Systematic Search for Changing-Look Quasars in SDSS. *Astrophys. J.*, 883(1), 76.

[7] Shu, X., Wang, J., Wang, T., et al. 2022. The Role of Tidal Disruption Events in Changing-look AGNs. *Astrophys. J.*, 924(2), 122.

[8] Frederick, S., Gezari, S., Graham, M. J., et al. 2019. Discovery of a Changing-look Quasar with PS1 and ZTF. *Astrophys. J.*, 883(1), L34.

[9] Cannizzaro, G., Gezari, S., Jonker, P. G., et al. 2022. Tidal Disruption Events and the Changing-look AGN Connection. *Astron. Astrophys.*, 665, A12.

[10] Panda, S., Czerny, B., Marziani, P., & Giustini, M. 2022. Disk Winds and Failed Winds in AGNs. *Frontiers in Astronomy and Space Sciences*, 9, 23.

[11] Giustini, M., & Proga, D. 2019. The X-ray emission from changing-look AGNs: insights from a simple model. *MNRAS*, 490, 1311-1323.

[12] Matt, G., Kara, E., & Chartas, G. 2023. Corona and Disk Wind Interactions in CL-AGN X-ray Variability. *MNRAS*, 518(3), 2891-2900.

[13] Shen, Y., Grier, C.J., Horne, K. 2021. The Sloan Digital Sky Survey Reverberation Mapping Project: Final Broad-line Hβ and Mg II Lags and Their Dependencies for 349 Quasars. *Astrophys. J. Suppl. Ser.*, 257(1), 36.

[14] Lawrence, A. 2018. Changing Look Quasars. *Nature Astronomy*, 2, 102-103.

[15] Shu, X., Wang, J., Du, P., et al. 2023. Revisiting the Disk-Wind Model in CL-AGN Transitions. *MNRAS*, 519(1), 134-150.

[16] Kara, E., Reynolds, C. S., & Dai, J. 2022. X-ray Time Lags as Probes of Black Hole Accretion in Changing-look AGNs. *Nature Astronomy*, 6, 787-794.

[17] Gunn, J. E., Siegmund, W. A., Mannery, E. J., et al. 2006. The SDSS Photometric Camera. *Astron. J.*, 131, 233-252.

[18] Cui, X., Zhao, Y., & Cheng, S. 2012. The LAMOST Pilot Survey: Overview and Preliminary Results. *Res. Astron. Astrophys.*, 12, 1197-1208.

[19] Zhao, Y., Cui, X., & Wang, J. 2012. The LAMOST Spectroscopic Survey: Overview and Preliminary Results. *Res. Astron. Astrophys.*, 12, 1243-1256.

[20] Du, P., Wang, J.-M., & Zhang, Z.-X. 2016. The broad emission line region in active galactic nuclei. *Astrophys. J. Suppl. Ser.*, 227, 27.

[21] Luo, A., Zhang, H.-T., & Wang, J.-M. 2012. The LAMOST Spectroscopic Data Processing. *Res. Astron. Astrophys.*, 12, 1243-1256.

[22] Ai, Y. L., Zhang, J. S., & Wang, J.-M. 2016. The LAMOST Quasar Catalog. *Astron. J.*, 151, 24.

[23] Dong, X.-B., Wang, J.-M., & Zhang, Z.-X. 2018. The LAMOST Quasar Survey II: New Quasar Candidates from LAMOST. *Astron. J.*, 155, 189.

[24] Elitzur, M., Ho, L. C., & Trump, J. R. 2014. Evolution of active galactic nuclei and their dusty tori.

[25] Shen, Y., & Liu, X. 2012. The Sizes of the Broad-line Region and Black Hole Masses of Moderate-luminosity Active Galactic Nuclei. *Astrophys. J.*, 753(2), 125.

[26] Matt, G., Guainazzi, M., & Maiolino, R. 2003. Compton-thick AGN: The dark side of the X-ray background. *MNRAS*, 342(2), 422-428.

[27] Elitzur, M., & Netzer, H. 2016. AGN Winds and the Role of Radiation Pressure. *MNRAS*, 459(2), 2102-2109.

[28] MacLeod, C. L., Ross, N. P., Lawrence, A., et al. 2016. The Nature of High-amplitude Quasar Variability in SDSS Stripe 82. *MNRAS*, 457(4), 3896-3916.

[29] Runnoe, J. C., Eracleous, M., Mathes, G., et al. 2016. The Disappearance of the Broad-line Region in a Changing-look Quasar. *MNRAS*, 455(2), 1691-1704.