TITLE: GCN CIRCULAR NUMBER: 39666 SUBJECT: IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations DATE: 25/03/11 11:59:31 GMT FROM: Ichiro Takahashi at Science Tokyo itakahashi@hp.phys.titech.ac.jp

Ichiro Takahashi (Science Tokyo), Kenta Taguchi (Kyoto U.), Seiji Toshikage, Masaomi Tanaka (Tohoku U.), Yousuke Utsumi (NAOJ), Ryosuke Itoh (Ibara City), Tomoki Morokuma (ARC/Chitech) report on behalf of a larger collaboration:

We performed optical imaging observations of the localization area of IceCube-250309A (GCN 39631) using the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno and the Tricolor CMOS Camera and Spectrograph (TriCCS) on the 3.8-m Seimei telescope. We started our observations at UT 2025-03-09 14:29 (MITSuME) and 2025-03-09 16:53 (Seimei), about 6.9 and 9.3 hours after the event, respectively. The observations with MITSuME covered the 90% probability region with 4 pointings while the observations with Seimei covered about half of the 90% probability region with 15 pointings. The data reduction and detailed examination of the data are underway.

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