| Author(s) and Co-Author(s) with Affiliation: Narendranath Layek(Physical Research Laboratory, Ahmedabad—380009, India), Sachindra Naik(Physical Research Laboratory, Ahmedabad—380009, India), Prantik Nandi(Indian Centre for Space Physics, Kolkata—700099, India), Birendra Chhotaray(Physical Research Laboratory, Ahmedabad—380009, India), Arghajit Jana(Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441,), Priyadarshee P. Dash(Physical Research Laboratory, Ahmedabad—380009, India), Neeraj Kumari(INAF-IASF Palermo, Via Ugo La Malfa 153, I-90146 Palermo, Italy), C. S. Stalin(Indian Institute of Astrophysics, Bangalore - 560034, India), Srikanth Bandari(Indian Institute of Astrophysics, Bangalore - 560034, India), S. Muneer(Indian Institute of Astrophysics, Bangalore - 560034, India) |
| Abstract: Active galactic nuclei (AGNs) are the most luminous and energetic sources in the universe, powered by the accretion of matter onto the supermassive black holes located at the centers of the host galaxies. Here, we present 17 years (2008–2025) of X-ray, UV, and optical observations, incorporating data from Swift, XMM-Newton, and NuSTAR, as well as optical data from the Very Large Telescope and the Himalayan Chandra Telescope (HCT) at Hanley, for the AGN NGC 3822. Optical spectroscopic monitoring of NGC 3822 reveals variation in emission lines over time. The 2018 spectrum shows only narrow Balmer emission (Hβ and Hα), whereas the 2022 spectra reveal clear broad Hβ and Hα components, confirming a type transition from type 2 to type 1. Subsequent HCT monitoring from July 2024 to July 2025 shows that the broadness of the Hβ and Hα lines significantly decreased, indicating that the source is transitioning back toward a type 2 state. Optical spectroscopic monitoring confirms the changing-look nature of NGC 3822, characterized by the appearance and disappearance of BELs in the spectra. These CL transitions are driven by changes in the mass accretion rate rather than variable obscuration. The BELs appear only when the Eddington ratio is relatively high (∼3.8 × 10-3) and disappear when it drops to a lower value (∼0.9 × 10-3). The multi-wavelength light-curve analysis reveals significant flux variability across the X-ray to optical/UV bands. A sudden outburst is observed during the 2022 epoch, which could be linked to a tidal disruption event, and its signature is also seen in the 2022 optical spectra. X-ray spectral analysis reveals intrinsic absorption in this AGN in 2016 and 2022, likely due to clouds moving into the line of sight, which subsequently moved out of the way before and after these epochs. |
