Swift detection of the Seyfert 1.9 galaxy IC 3599 in a bright X-ray state.

ATel #17479; D. Grupe (Northern Kentucky University), S. Komossa (MPIfR, NAOC), S. Wolsing (U. Goettingen), and N. Schartel
on 6 Nov 2025; 02:40 UT
Credential Certification: Dirk Grupe (dgrupe007@gmail.com)

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We are reporting on a rebrightening of the Seyfert 1.9 galaxy IC 3599 detected by Swift. IC 3599 just emerged from its Swift sun-constraint on October 31. During this observation, Swift found this AGN at a 0.3-10 keV flux of 7e-15 W/m^2 displaying a very steep X-ray spectrum with Gamma=5.0+/-0.4. In our most recent observation from November 05, the flux slightly increased to 1.4e-14 W/m^2 with Gamma = 3.5+/-0.2. The observations are part of our ongoing long-term monitoring project of IC 3599 (Grupe et al. 2015, 2024) and IC 3599 has shown bright outbursts in the past, the first of these during the RASS in 1990 (Grupe et al. 1995,Brandt et al. 1995).

With Swift's UVOT, on November 05, we measured the following magnitudes in the VEGA system: UVW2: 16.21+/-0.05 (16.07), UVM2: 16.25+/-0.07 (16.10), UVW1: 16.10+/-0.06 (16.00), U: 16.15+/-0.06 (16.07), B: 16.35+/-0.06 (16.28), and V: 15.75+/-0.07 (15.70) with reddening-corrected values in brackets. These values are about 0.2 mag brighter than during the low state.

We will continue monitoring IC 3599 with Swift and have triggered an observation with XMM-Newton and further MWL follow-up observations. We would like to thank Brad Cenko for approving our observing requests and the Swift team for promptly executing the observations.