{
  "bibcode": "2022GCN.33087....1T",
  "body": "I. Takahashi, M. Niwano, R. Hosokawa, K. L. Murata, Y. Imai, N. Ito,\nS. Sato, N. Higuchi, M. Tateda, M. Sasada, Y. Yatsu, and N. Kawai\n(Tokyo Tech) report on behalf of the MITSuME collaboration:\n\nWe observed the field of GRB 221218A (S. Mereghetti et al. GCN\nCircular #33082, WeiKang Zheng et al. GCN Circular #33085, Y.-D. Hu et\nal. GCN Circular #33086) with the optical three color (g', Rc, and Ic)\nCCD cameras attached to the MITSuME 50 cm telescope Akeno.\n\nThe observation with a series of 60 sec exposures started at\n2022-12-18 08:37:35 UT (1405 seconds after the INTEGRAL trigger). We\nstacked the images with good conditions. We did not detect any\nuncatalogued sources within the error region (S. Mereghetti et al. GCN\nCircular #33082). We obtained the 5-sigma limits of the stacked images\nas follows.\n\nT0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits\n------------------------------------------------------------------------------------------------\n1405 | 2022-12-18 08:51:23 | 1140.0 | g'>19.1, Rc>19.0, Ic>18.4\n------------------------------------------------------------------------------------------------\nT0+ : Elapsed time after the burst\nT-EXP: Total Exposure time\n\nWe used PS1 catalog for flux calibration. The magnitudes are expressed\nin the AB system. The images were processed in real-time through the\nMITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73,\nIssue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).",
  "circularId": 33087,
  "createdOn": 1671531675000,
  "email": "itakahashi@hp.phys.titech.ac.jp",
  "subject": "GRB 221218A: MITSuME Akeno optical upper limits",
  "submitter": "Ichiro Takahashi at Tokyo Tech  <itakahashi@hp.phys.titech.ac.jp>",
  "eventId": "GRB 221218A"
}