{
  "bibcode": "2021GCN.30096....1M",
  "body": "K. L. Murata, R. Hosokawa, M. Niwano, Y. Imai, N. Ito, H. Takamatsu, S.\nSato, M. Takaku, R. Noto, R. Yamaguchi, Y. Yatsu, and N. Kawai (TokyoTech)\nreport on behalf of the MITSuME collaboration:\n\nWe observed the field of GRB 210528B (Sugawara et al. GCN Circular #30094,\nLipunov et al. GCN Circular #30095) with the optical three color (g', Rc,\nand Ic) CCD cameras attached to the MITSuME telescope Akeno. The\nobservation with a series of 60 sec exposures started at 2021-05-29\n11:21:57 UT (12.5 hours after the trigger). We stacked the images with good\nconditions. We did not detect any uncatalogued sources in all three bands\nwithin the elliptical error region (Sugawara et al. GCN Circular #30094)\ndetermined under the assumption that the source flux was constant over the\ntransit. We obtained the 5-sigma limits of the stacked images as follows.\n\nT0+[hour] MID-UT T-EXP[sec] 5-sigma limits\n------------------------------------------------------------------------------------------------\n12.5 2021-05-29 12:13 1560 g'>19.9\n12.5 2021-05-29 12:13 2040 Rc>20.2\n12.5 2021-05-29 12:13 1500 Ic>19.4\n------------------------------------------------------------------------------------------------\nT0+ : Elapsed time after the burst\nT-EXP: Total Exposure time\nWe used the 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 1,\nPages 4-24; https://github.com/MNiwano/Eclaire).",
  "circularId": 30096,
  "createdOn": 1622296653000,
  "email": "murata@u.phys.nagoya-u.ac.jp",
  "subject": "GRB 210528B: MITSuME Akeno optical upper limits",
  "submitter": "Katsuhiro L. Murata at Nagoya U  <murata@u.phys.nagoya-u.ac.jp>",
  "eventId": "GRB 210528B"
}