Tracing active galactic nuclei properties through a changing-look event

Abstract

Changing-look transitions challenge our understanding of active galactic nuclei (AGNs), exhibiting dramatic changes in broad-line emission and continuum flux on time-scales of months to years. We present a detailed study of the spectroscop- ically confirmed changing-look AGN ZTF18abuamgo. Combining photometric survey data with spectroscopy spanning three epochs over 20 yr, we identify a turn-on transition from a Type 1.5 to Type 1.2 AGN and estimate the time-scale of this change to be as short as 4 yr. Spectral analysis indicates that this transformation is driven by a rapid increase in accretion rat e, with the Eddingt on ratio rising from 0 . 032 ± 0 . 005 in the dim stat e t o 0 . 08 ± 0 . 01 in the bright state. For the first time in a changing-look AGN, we apply the Boltzmann plot method to the visible Balmer series emission, deriving broad-line r egion electr on temperatur es of 11 800 ± 900 and 11 900 ± 2400 K in 2022 and 2024, respectively. Applying single-epoch black hole mass estimation to the brightening H α emission, we find a mass of (5 . 0 ± 0 . 4) × 10 7 M ⊙. The consistency in this estimate across all spectroscopic epochs suggest that even highly variable broad lines in CL-AGN do not bias the results derived using this method. Our results demonstrate that objects like ZTF18abuamgo provide a unique laboratory to study e xtr eme AGN variability, pr obe the physical conditions in the br oad-line r egion, and assess the limitations of widely used black hole mass estimation methods.

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ORCID for Sandra Raimundo: orcid.org/0000-0002-6248-398X

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