Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert

Saha T, Markowitz A, Homan D, Krumpe M, Hämmerich S, Czerny B, Graham M, Frederick S, Gromadzki M, Gezari S, Winkler H, Buckley DA, Brink J, Naddaf MH, Rau A, Wilms J, Gokus A, Liu Z, Grotova I (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Astronomy & Astrophysics EDP Sciences

Book Volume: 702

Article Number: A28

DOI: 10.1051/0004-6361/202347985

Abstract

Context. Multiwavelength studies of transients in actively accreting supermassive black holes have revealed that large-amplitude variability is frequently linked to significant changes in the optical spectra. This phenomenon is known as a changing-look active galactic nucleus (CLAGN). Aims. In 2020, the Zwicky Transient Facility detected a transient flaring event in the type 1.9 AGN LEDA 1154204, wherein the brightness sharply increased by 0.55 mag in one month and then began to decay. Spectrum Roentgen Gamma (SRG)/eROSITA also observed the object as part of its all-sky X-ray surveys after the flare had started to decay. Methods. We performed a three-year multiwavelength follow-up campaign to track the spectral and temporal characteristics of the source during the post-flare fading. This campaign included optical spectroscopy, X-ray spectroscopy and photometry, and ultraviolet, optical, and infrared continuum photometry. Results. Optical spectra taken near the flare peak revealed a broad double-peaked Hβ emission and a blue continuum, neither of which were detected in a 2005 archival spectrum. The broad Hβ had increased by a factor of > 5–6. From late 2020 through 2023, the broad Balmer-line flux faded as the continuum faded, and the Balmer decrement increased by ∼2.2. This is consistent with the expected ionization response. The X-ray spectrum exhibits no significant spectral variability despite dramatic flux variation of a factor of 17. There is no evidence of a soft X-ray excess, which indicates an energetically unimportant warm corona. Conclusions. The transient event was likely triggered by a disk instability in a preexisting AGN-like accretion flow that culminated in the observed multiwavelength variability (X-rays via thermal Comptonization, illumination of the broad-line region, and infrared dust echo) and in the CLAGN event.

Authors with CRIS profile

Steven Hämmerich Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut Jörn Wilms Professur für Astronomie und Astrophysik Andrea Gokus Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut

Involved external institutions

Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences PL Poland (PL) Leibniz Institute for Astrophysics Potsdam / Leibniz-Institut für Astrophysik Potsdam DE Germany (DE) Center for Theoretical Physics of the Polish Academy of Sciences PL Poland (PL) California Institute of Technology (Caltech) US United States (USA) (US) University of Maryland, College Park (UMD) US United States (USA) (US) University of Warsaw / Uniwersytet Warszawski PL Poland (PL) Space Telescope Science Institute (STScI) US United States (USA) (US) University of Johannesburg ZA South Africa (ZA) South African Astronomical Observatory (SAAO) ZA South Africa (ZA) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics DE Germany (DE)

How to cite

APA:

Saha, T., Markowitz, A., Homan, D., Krumpe, M., Hämmerich, S., Czerny, B.,... Grotova, I. (2025). Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert. Astronomy & Astrophysics, 702. https://doi.org/10.1051/0004-6361/202347985

MLA:

Saha, T., et al. "Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert." Astronomy & Astrophysics 702 (2025).

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