Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert
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| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2023
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| _version_ | 1866918121395191808 |
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| author | Saha, T. Markowitz, A. Homan, D. Krumpe, M. Haemmerich, S. Czerny, B. Graham, M. Frederick, S. Gromadzki, M. Gezari, S. Winkler, H. Buckley, D. A. H. Brink, J. Naddaf, M. H. Rau, A. Wilms, J. Gokus, A. Liu, Z. Grotova, I. |
| author_facet | Saha, T. Markowitz, A. Homan, D. Krumpe, M. Haemmerich, S. Czerny, B. Graham, M. Frederick, S. Gromadzki, M. Gezari, S. Winkler, H. Buckley, D. A. H. Brink, J. Naddaf, M. H. Rau, A. Wilms, J. Gokus, A. Liu, Z. Grotova, I. |
| contents | 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 -- a phenomenon known as changing-look AGN (CLAGN).} Aims. In 2020, the Zwicky Transient Facility detected a transient flaring event in the type 1.9 AGN LEDA 1154204, wherein brightness sharply increased by 0.55 mag in one month, 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 decaying. Methods. We performed a three-year, multiwavelength follow-up campaign to track the source's spectral and temporal characteristics, during the post-flare fading. This campaign included optical spectroscopy, X-ray spectroscopy and photometry, and UV, optical, and IR continuum photometry. Results. Optical spectra taken near the flare peak revealed a broad double-peaked H$β$ emission and a blue continuum, both undetected in a 2005 archival spectrum; broad H$β$ had increased by a factor $>$5--6. Then, from late 2020 through 2023, broad Balmer line flux faded as the continuum faded, with Balmer decrement increasing by $\sim$2.2, consistent with the expected ionization response. The X-ray spectrum exhibits no significant spectral variability despite dramatic flux variation -- a factor of 17. There is no evidence of a soft X-ray excess, indicating an energetically unimportant warm corona. Conclusions. The transient event was likely triggered by a disk instability in a pre-existing AGN-like accretion flow, culminating in the observed multiwavelength variability -- X-rays via thermal Comptonization, BLR illumination, and IR dust echo -- and CLAGN event. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2309_08956 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | 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. Haemmerich, S. Czerny, B. Graham, M. Frederick, S. Gromadzki, M. Gezari, S. Winkler, H. Buckley, D. A. H. Brink, J. Naddaf, M. H. Rau, A. Wilms, J. Gokus, A. Liu, Z. Grotova, I. High Energy Astrophysical Phenomena 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 -- a phenomenon known as changing-look AGN (CLAGN).} Aims. In 2020, the Zwicky Transient Facility detected a transient flaring event in the type 1.9 AGN LEDA 1154204, wherein brightness sharply increased by 0.55 mag in one month, 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 decaying. Methods. We performed a three-year, multiwavelength follow-up campaign to track the source's spectral and temporal characteristics, during the post-flare fading. This campaign included optical spectroscopy, X-ray spectroscopy and photometry, and UV, optical, and IR continuum photometry. Results. Optical spectra taken near the flare peak revealed a broad double-peaked H$β$ emission and a blue continuum, both undetected in a 2005 archival spectrum; broad H$β$ had increased by a factor $>$5--6. Then, from late 2020 through 2023, broad Balmer line flux faded as the continuum faded, with Balmer decrement increasing by $\sim$2.2, consistent with the expected ionization response. The X-ray spectrum exhibits no significant spectral variability despite dramatic flux variation -- a factor of 17. There is no evidence of a soft X-ray excess, indicating an energetically unimportant warm corona. Conclusions. The transient event was likely triggered by a disk instability in a pre-existing AGN-like accretion flow, culminating in the observed multiwavelength variability -- X-rays via thermal Comptonization, BLR illumination, and IR dust echo -- and CLAGN event. |
| title | Multiwavelength study of extreme variability in LEDA 1154204: A changing-look event in a type 1.9 Seyfert |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2309.08956 |