Follow-up optical spectroscopy of the changing-look AGN IC 3599 in an X-ray, UV, and optical high-state
ATel #17507; S. Komossa (MPIfR), D. Grupe (NKU), W. Zheng (UCB), T. G. Brink (UCB), A. V. Filippenko (UCB), E. Elien (UCLA), C. Tapper (UCLA), P. Lynam (Lick), J. Wang (NAOC), N. Schartel (ESA), S. Wolsing (U Goettingen), V. Oknyansky (SAI)
on 28 Nov 2025; 02:00 UT
Credential Certification: St. Komossa (stefanie.komossa@gmx.de)
Subjects: Optical, Ultra-Violet, X-ray, AGN
We report on follow-up optical spectroscopy of the Seyfert 1.9 galaxy IC 3599 (z=0.021) that was recently found in an X-ray-UV-optical high-state with the Neil Gehrels Swift observatory based on a dedicated monitoring program (ATel #17479, Grupe et al. 2025). Enhanced optical emission was confirmed by Veres 2025 (ATel #17483).
Optical spectroscopy was carried out on 2025 November 22.54 UT using the Kast double spectrograph at the Cassegrain focus of the Shane 3 m telescope at Lick observatory. The spectra show a significant increase in the broad Balmer lines as well as in high-ionization forbidden line transitions, including [FeXIV]5303 and [FeX]6374. IC 3599 has changed from a Seyfert 1.9 AGN in low-state (Komossa & Bade 1999) to a Seyfert 1 AGN in high-state.
Further optical spectroscopy is planned.
Our dedicated ongoing Swift observations show that the high-state continues in all UVOT bands and in the X-ray regime. The last observation was carried out on November 26.
IC 3599 is an optical changing-look AGN highly variable in the X-ray regime that is well explained by an accretion-disk instability scenario (e.g., Grupe et al. 2015, 2024, Komossa & Grupe 2024). We would like to thank the Swift team for approving and carrying out the observations we proposed, and the Lick observatory staff for performing the ToO observations.
