Extreme Multiwavelength Variability in the Recurrent Intermediate-type Changing-look Seyfert Galaxy SDSS J234728.73+242745.7
Abstract
We report the discovery of the Seyfert galaxy J234728.73+242745.7 as a recurrent intermediate-type CLAGN with extreme optical/UV variability. Optical spectra spanning nearly three decades reveal Type 1.0→1.5→1.2 transitions, accompanied by the disappearance and reappearance of broad He II λ4686 and a broad-line Balmer decrement evolving from 4.5 to 7.2 and then 2.4. Monitoring reveals coordinated variability from X-rays to the MIR. SED decomposition yields a host-corrected g-band high-to-low-state flux ratio of 5.4±0.4, exceeding the Swift/XRT ratio of 2.7±0.8 across the changing-look transition. This discrepancy may arise from reduced dust extinction, as correcting for the low-state continuum reddening (AVcont=0.66±0.23 mag) brings the optical/UV ratios close to the X-ray value, although the correction is model-dependent and intrinsically weaker X-ray variability may also contribute. However, X-ray spectra show no compelling evidence for intrinsic gas absorption or its variability (NHintr≲5×1020 cm−2). In contrast, EP/WXT monitoring during the recent high state reveals order-of-magnitude X-ray fluctuations on monthly-to-sub-year timescales, exceeding contemporaneous optical variations. Meanwhile, the radio flux density remains stable at ∼2 mJy across all ASKAP observations since mid-2020. Together with optical/UV and MIR variability and the broad He II transition, these results favor intrinsic accretion-state changes as the primary driver, while allowing a secondary contribution from variable obscuration. The source displays a loop-like MIR color--magnitude evolution, likely driven by the delayed response of an extended torus. This recurrent CLAGN offers a laboratory for probing the dynamic response of the broad-line region and circumnuclear dust to accretion-state transitions.
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BibTeX
@misc{wu2026extreme,
title = {{Extreme Multiwavelength Variability in the Recurrent Intermediate-type Changing-look Seyfert Galaxy SDSS J234728.73+242745.7}},
author = {Jiahua Wu and Liming Dou and Yanli Ai and Jianguo Wang and Tinggui Wang and Huaqing Cheng and Chichuan Jin and Luis C. Ho and Qiming Wu and Kovi Rose and Roberto Soria and Alexis Coleiro and Junhui Fan and Yuan Liu and Dongyue Li and Zhen Zhang and Yunfei Xu},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.04236},
eprint = {2611.04236},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.04236},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Extreme Multiwavelength Variability in the Recurrent Intermediate-type Changing-look Seyfert Galaxy SDSS J234728.73+242745.7
AU - Jiahua Wu
AU - Liming Dou
AU - Yanli Ai
AU - Jianguo Wang
AU - Tinggui Wang
AU - Huaqing Cheng
AU - Chichuan Jin
AU - Luis C. Ho
AU - Qiming Wu
AU - Kovi Rose
AU - Roberto Soria
AU - Alexis Coleiro
AU - Junhui Fan
AU - Yuan Liu
AU - Dongyue Li
AU - Zhen Zhang
AU - Yunfei Xu
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.04236
UR - https://arxiv.org/abs/2611.04236
AB - We report the discovery of the Seyfert galaxy J234728.73+242745.7 as a recurrent intermediate-type CLAGN with extreme optical/UV variability. Optical spectra spanning nearly three decades reveal Type 1.0→1.5→1.2 transitions, accompanied by the disappearance and reappearance of broad He II λ4686 and a broad-line Balmer decrement evolving from 4.5 to 7.2 and then 2.4. Monitoring reveals coordinated variability from X-rays to the MIR. SED decomposition yields a host-corrected g-band high-to-low-state flux ratio of 5.4±0.4, exceeding the Swift/XRT ratio of 2.7±0.8 across the changing-look transition. This discrepancy may arise from reduced dust extinction, as correcting for the low-state continuum reddening (A_V^cont=0.66±0.23 mag) brings the optical/UV ratios close to the X-ray value, although the correction is model-dependent and intrinsically weaker X-ray variability may also contribute. However, X-ray spectra show no compelling evidence for intrinsic gas absorption or its variability (N_H^intr≲5×10^20 cm^−2). In contrast, EP/WXT monitoring during the recent high state reveals order-of-magnitude X-ray fluctuations on monthly-to-sub-year timescales, exceeding contemporaneous optical variations. Meanwhile, the radio flux density remains stable at ∼2 mJy across all ASKAP observations since mid-2020. Together with optical/UV and MIR variability and the broad He II transition, these results favor intrinsic accretion-state changes as the primary driver, while allowing a secondary contribution from variable obscuration. The source displays a loop-like MIR color--magnitude evolution, likely driven by the delayed response of an extended torus. This recurrent CLAGN offers a laboratory for probing the dynamic response of the broad-line region and circumnuclear dust to accretion-state transitions.
ER -