{
  "bibcode": "2022GCN.32883....1N",
  "body": "M. Niwano, R. Hosokawa, I.Takahashi, K. L. Murata, Y. Imai, N. Ito, S. \nSato, N. Higuchi, M. Tateda, M. Sasada, Y. Yatsu, and N. Kawai (Tokyo \nTech) report on behalf of the MITSuME collaboration:\n\nWe observed the field of GRB 221028A (A. Y. Lien et al. GCN Circular \n#32874, H. Kumar et al. GCN Circular #32876, Y.-D. Hu et al. GCN \nCircular #32878, V. Lipunov et al. GCN Circular #32879, R. Strausbaugh \net al. GCN Circular #32881) with the optical three color (g', Rc, and \nIc) CCD cameras attached to the MITSuME 50 cm telescope Okayama.\n\nThe observation with a series of 60 sec exposures started at 2022-10-28 \n13:17:23 UT (59 seconds after the Swift/BAT trigger). We stacked the \nimages with good conditions. We did not detect any uncatalogued sources \nwithin the Swift/XRT error region (A. Y. Lien et al. GCN Circular \n#32874). We obtained the 5-sigma limits of the stacked images as follows.\n\nT0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits\n------------------------------------------------------------------------------------------------\n59 | 2022-10-28 14:17:10 | 5790.0 | g'>18.7, Rc>19.5, Ic>18.7\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, Issue \n1, Pages 4-24; https://github.com/MNiwano/Eclaire).",
  "circularId": 32883,
  "createdOn": 1667026935000,
  "email": "niwano@hp.phys.titech.ac.jp",
  "subject": "GRB 221028A: MITSuME Okayama optical upper limits",
  "submitter": "Masafumi Niwano at Tokyo Institute of Tech  <niwano@hp.phys.titech.ac.jp>",
  "eventId": "GRB 221028A"
}