{
  "bibcode": "2021GCN.29565....1H",
  "body": "R. Hosokawa, K. L. Murata, R. Adachi, M. Niwano, F. Ogawa, N.\nNakamura, N. Ito, S. Ogata, H. Takamatsu, H. Hara, Y. Yatsu, and N.\nKawai (TokyoTech) report on behalf of the MITSuME collaboration:\n\nWe observed the field of GRB 210222B (Lipunov et al. GCN #29544, Gropp\net al. GCN #29545, Hu et al. GCN #29546, Strausbaugh et al. GCN\n#29547, Mong et al. GCN #29548, Perley et al. GCN #29549, Mong et al.\nGCN #29550, Zhu et al. GCN #29551, Fernandez et al. GCN #29552,\nLipunov et al. GCN #29554, Jelinek et al. GCN #29557, Zheng et al. GCN\n#29558, Siegel et al. GCN #29559, Page et al. GCN #29560, Ukwatta et\nal. GCN #29561, Gokuldass et al. GCN #29562, Belkin et al. GCN #29563)\n with the optical three color (g', Rc, and Ic) CCD cameras attached to\nthe MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.\nThe observation with a series of 60 sec exposures started at\n2021-02-23 11:00:13 UT(12.4hours after the Swift BAT trigger). We\nstacked the images with good conditions. We did not detect the optical\nafterglow reported previously (Gropp et al. GCN #29545, Hu et al. GCN\n#29546, Strausbaugh et al. GCN #29547, Mong et al. GCN #29548, Perley\net al. GCN #29549, Mong et al. GCN #29550, Zhu et al. GCN #29551,\nFernandez et al. GCN #29552, Lipunov et al. GCN #29554, Jelinek et al.\nGCN #29557, Siegel et al. GCN #29559, Gokuldass et al. GCN #29562,\nBelkin et al. GCN #29563) in all three bands.\nWe obtained the 5-sigma limits of the stacked images as follows.\n\nT0+[hour] MID-UT T-EXP[sec] 5-sigma limits\n------------------------------------------------------------------------------------------------\n12.4 15:18:25 14100 g'>19.6, Rc>19.9, Ic>19.2\n------------------------------------------------------------------------------------------------\nT0+ : Elapsed time after the burst\nT-EXP: Total Exposure time\nWe used the PS1 catalog for flux calibration.\nThe magnitudes are expressed in the AB system.\nThe images were processed in real-time through the MITSuME GPU\nreduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages\n4-24; https://github.com/MNiwano/Eclaire).",
  "circularId": 29565,
  "createdOn": 1614241841000,
  "email": "hosokawa@hp.phys.titech.ac.jp",
  "subject": "GRB 210222B: MITSuME Akeno optical upper limits",
  "submitter": "Ryohei Hosokawa at Tokyo Institute of Technology  <hosokawa@hp.phys.titech.ac.jp>",
  "eventId": "GRB 210222B"
}