TITLE: GCN CIRCULAR NUMBER: 31310 SUBJECT: GRB 211225A: MITSuME Akeno optical upper limits DATE: 21/12/26 13:16:55 GMT FROM: Naohiro Ito at Tokyo Tech N. Ito, R. Hosokawa, M. Niwano, K. L. Murata, Y. Imai, Y. Takamatsu, R. Yamaguchi, R. Noto, S. Sato, M. Takaku, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We performed tiling observations for the MAXI/GSC error region of GRB 211225A, MAXI J0827-071 (T. Kurihara et al. GCN Circular #31303, V. Lipunov et al. GCN Circular #31304) with an optical tri-color (g', Rc, and Ic) camera attached to the MITSuME 50 cm telescope Akeno. The follow up observation started at 2021-12-25 12:43:40 UT, 9.4 hours after the trigger. Our tiling observation covered almost ~90% of the MAXI/GSC elliptical error region (GCN Circular #31303). Comparing our co-added images with the GSC2.3 catalog, we found no optical transients in the observed region. The 5-sigma upper limits of the co-added images are listed below. Field num. | center position (R.A., Dec.) | size of field (R.A.(arcmin) x Dec.(arcmin)) | 5-sigma upper limit | MID-UT (UT) | exposure time (sec) -------------------------------------------------------------------------------------------------------------------------- Field 00 | 8:27:04, -7:19:28 | 25.1 x 24.8 | g'>18.1, Rc>18.4, Ic>17.9 | 2021-12-25 15:30:02 | 1260 Field 01 | 8:28:39, -7:19:27 | 26.1 x 25.1 | g'>18.1, Rc>18.4, Ic>17.6 | 2021-12-25 15:36:28 | 1380 Field 02 | 8:27:01, -6:54:21 | 26.3 x 24.0 | g'>18.3, Rc>18.7 | 2021-12-25 16:31:42 | 2400 Field 03 | 8:28:37, -6:54:57 | 26.3 x 24.6 | g'>18.0, Rc>18.4, Ic>17.8 | 2021-12-25 16:48:59 | 1620 -------------------------------------------------------------------------------------------------------------------------- We used PS1 catalog for flux calibration. 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, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).