{
  "bibcode": "2021GCN.29936....1H",
  "body": "R. Hosokawa, K. L. Murata, M. Niwano, N. Ito, H. Takamatsu, Y. Imai,\nS. Sato, M. Takaku, R. Noto, R. Yamaguchi, Y. Yatsu, and N. Kawai\n(TokyoTech) report on behalf of the MITSuME collaboration:\n\nWe observed the field of GRB 210504A (Beardmore et al. GCN Circular #29929, Lien\n et al. GCN Circular #29930) with the optical three color (g', Rc, and\nIc) CCD cameras attached to the MITSuME 50 cm telescope of Akeno\nObservatory, Yamanashi, Japan. The observation with a series of 60 sec\nexposures started at 2021-05-04 14:55:16 UT (1.0 hour after the BAT\ntrigger, Lien et al. GCN Circular #29930). We stacked the images with\ngood conditions. We did not detect any uncatalogued sources within the\nXRT error circle (Beardmore et al. GCN Circular #29929) in all three\nbands. We obtained the 5-sigma limits of the stacked images as\nfollows.\n\nT0+[hour] MID-UT T-EXP[sec] 5-sigma limits\n------------------------------------------------------------------------------------------------\n1.1 2021-05-04 15:01 300 g���>15.9, Rc>16.2, Ic>15.9\n2.8 2021-05-04 16:42 2580 g���>18.3, Rc>18.7, Ic>18.3\n------------------------------------------------------------------------------------------------\nT0+ : Elapsed time after the burst\nT-EXP: Total Exposure time\n\nWe used the PS1 catalog for flux calibration. The magnitudes are\nexpressed in the AB system. The images were processed in real-time\nthrough the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ,\nVol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).",
  "circularId": 29936,
  "createdOn": 1620171354000,
  "email": "hosokawa@hp.phys.titech.ac.jp",
  "subject": "GRB 210504A: MITSuME Akeno optical upper limits",
  "submitter": "Ryohei Hosokawa at Tokyo Institute of Technology  <hosokawa@hp.phys.titech.ac.jp>",
  "eventId": "GRB 210504A"
}