TITLE: GCN CIRCULAR NUMBER: 43029 SUBJECT: GRB 251205A : MITSuME Akeno optical afterglow candidate detection DATE: 25/12/08 10:54:40 GMT FROM: hagio.h.ffca@m.isct.ac.jp H. Hagio, Y. Kubo, I. Takahashi, M. Sasada, H. Seki, A. Ochi, R. Kato, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 251205A detected by Swift (Lanava et al., GCN 43005) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-12-06 16:56:58 UT (16.3 hr after the trigger). We stacked the images taken under good conditions. We detected a point source in the Rc- and Ic-band images at a position of the reported optical candidate (Lipunov et al., GCN 43004; Lanava et al., GCN 43005; Lipunov et al., GCN 43006; Malesani et al., GCN 43009; O'Neill et al., GCN 43010; Mandarakas et al., GCN 43011; Pankov et al., GCN 43012; Bochenek et al., GCN 43015; Klingler et al., GCN 43016; Patil et al., GCN 43019; Pérez-Fournon et al., GCN 43020; Bochenek et al., GCN 43024; Busmann et al., GCN 43026 ). Our photometric results can be contaminated by the flux from the nearby galaxy. Here we report the preliminary magnitudes of the source as follows. T0+[sec] | MID-UT | T-EXP[sec] | magnitudes --------------------------------------------------------------------------------------------------------------- 68759 | 2025-12-06 18:45:46 | 4860 | Rc=19.1+/-0.2, Ic=18.8+/-0.2 --------------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire). View this GCN Circular online at https://gcn.nasa.gov/circulars/43029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...