TITLE: GCN CIRCULAR NUMBER: 31278 SUBJECT: GRB 211218A: MITSuME Akeno optical upper limits DATE: 21/12/22 11:58:51 GMT FROM: Yuri Imai at Tokyo Inst of Tech Y. Imai, R. Hosokawa, K. L. Murata, M. Niwano, Y. Takamatsu, N. Ito, R. Yamaguchi, R. Noto, S. Sato, M. Takaku, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We performed tiling observations for the MAXI/GSC error region of GRB 211218A, MAXI J0909-041 (R. Uematsu et al. GCN Circular #31261, V. Lipunov et al. GCN Circular #31260) with an optical tri-color (g', Rc, and Ic) camera attached to the MITSuME 50 cm telescope Akeno. The follow up observation started at 2021-12-18 13:35:14 UT, 12.6 hours after the trigger. Our tiling observation covered almost ~70% of the MAXI/GSC error region (GCN Circular #31261). 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 | 9:08:47, -4:06:36 | 27.1 x 24.7 | g'>18.2, Rc>19.0, Ic>18.7 | 2021-12-18 17:57:09 | 360.0 Field 01 | 9:08:01, -4:22:05 | 26.6 x 26.5 | g'>18.3, Rc>19.1, Ic>18.7 | 2021-12-18 17:19:28 | 390.0 Field 02 | 9:09:42, -4:17:55 | 26.4 x 26.5 | g'>18.2, Rc>19.0, Ic>18.6 | 2021-12-18 17:45:57 | 330.0 Field 03 | 9:09:01, -4:31:20 | 27.4 x 24.2 | g'>18.2, Rc>19.0, Ic>18.6 | 2021-12-18 17:37:16 | 330.0 Field 04 | 9:07:45, -3:55:46 | 26.0 x 24.3 | g'>18.3, Rc>19.2, Ic>18.8 | 2021-12-18 16:58:53 | 450.0 Field 05 | 9:07:04, -4:08:57 | 26.5 x 27.5 | g'>17.9, Rc>18.7, Ic>18.4 | 2021-12-18 15:49:39 | 240.0 Field 06 | 9:09:26, -3:51:26 | 26.2 x 25.5 | g'>18.2, Rc>18.9, Ic>18.6 | 2021-12-18 17:24:50 | 360.0 Field 07 | 9:07:20, -4:34:20 | 26.5 x 26.1 | g'>18.0, Rc>18.7, Ic>18.4 | 2021-12-18 17:04:52 | 240.0 Field 08 | 9:10:28, -4:03:20 | 26.6 x 26.5 | g'>18.3, Rc>19.2, Ic>18.8 | 2021-12-18 16:49:06 | 540.0 Field 09 | 9:08:17, -4:47:13 | 26.4 x 26.7 | g'>18.1, Rc>18.9, Ic>18.5 | 2021-12-18 17:33:11 | 300.0 Field 10 | 9:08:29, -3:40:30 | 26.5 x 25.1 | g'>18.3, Rc>19.0, Ic>18.7 | 2021-12-18 17:11:30 | 390.0 Field 11 | 9:06:22, -4:25:47 | 25.8 x 26.1 | g'>18.2, Rc>19.1, Ic>18.7 | 2021-12-18 16:00:21 | 480.0 Field 12 | 9:10:10, -3:37:09 | 26.3 x 26.7 | g'>18.0, Rc>18.9, Ic>18.6 | 2021-12-18 16:24:58 | 300.0 Field 13 | 9:06:39, -4:50:05 | 26.4 x 26.6 | g'>17.9, Rc>18.8, Ic>18.4 | 2021-12-18 15:17:23 | 270.0 Field 14 | 9:11:06, -3:48:44 | 26.6 x 26.5 | g'>18.1, Rc>18.8, Ic>18.4 | 2021-12-18 17:11:04 | 210.0 Field 15 | 9:09:11, -3:27:56 | 26.0 x 26.9 | g'>18.1, Rc>19.0, Ic>18.6 | 2021-12-18 16:13:00 | 330.0 Field 16 | 9:07:35, -5:00:29 | 27.3 x 27.6 | g'>17.7, Rc>18.5, Ic>18.3 | 2021-12-18 15:36:49 | 180.0 Field 17 | 9:05:40, -4:40:29 | 27.2 x 26.4 | g'>18.0, Rc>18.8, Ic>18.6 | 2021-12-18 16:07:28 | 330.0 Field 18 | 9:10:52, -3:22:30 | 26.4 x 26.5 | g'>18.0, Rc>18.9, Ic>18.5 | 2021-12-18 15:30:13 | 300.0 Field 19 | 9:11:49, -3:34:14 | 26.6 x 26.5 | g'>18.0, Rc>18.7, Ic>18.4 | 2021-12-18 16:57:19 | 180.0 Field 20 | 9:05:56, -5:04:58 | 26.5 x 26.6 | g'>18.1, Rc>19.0, Ic>18.6 | 2021-12-18 17:02:01 | 420.0 Field 21 | 9:09:48, -3:03:38 | 28.5 x 28.6 | g'>17.1, Rc>17.8, Ic>17.4 | 2021-12-18 20:31:34 | 60.0 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 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).