{
  "bibcode": "2021GCN.31217....1I",
  "body": "N. Ito, R. Hosokawa, K. L. Murata, Y. Imai, Y. Takamatsu, M. Takaku, M.\nNiwano, R. Noto, S. Sato, R. Yamaguchi, Y. Yatsu, and N. Kawai (TokyoTech)\nreport on behalf of the MITSuME collaboration:\n\nWe observed the field of GRB 211211A (The Fermi GBM team GCN Circular\n#31201, A. D'Ai et al. GCN Circular #31202, WeiKang Zheng and Alexei V.\nFilippenko GCN Circular #31203, A.P. Beardmore et al. GCN Circular #31205,\nV. Lipunov et al. GCN Circular #31206, M. Stamatikos et al. GCN Circular\n#31209, J.Mangan et al. GCN Circular #31210, J.P. Osborne et al. GCN\nCircular #31212, S.Q. Jiang et al. GCN Circular #31213, R. Strausbaugh and\nA. Cucchiara GCN Circular #32214) with the optical three color (g', Rc, and\nIc) CCD cameras attached to the MITSuME 50 cm telescope Akeno. The\nobservation with a series of 60 sec exposures was carried out from\n2021-12-11 17:32:12 UT (~4.4 hours after the Fermi trigger) to 2021-12-11\n21:20:21 UT. We stacked the images with good conditions.\n\nWe marginally detected the optical afterglow candidate reported by the KAIT\nobservation (WeiKang Zheng and Alexei V. Filippenko GCN Circular #31203),\nNanshan/NEXT observation (S.Q. Jiang et al. GCN Circular #31213) and LCO\nobservation (R. Strausbaugh and A. Cucchiara GCN Circular #32214) in our\ng'-, Rc- and Ic- band images. The candidate in our images is blended with\nthe nearby SDSS galaxy (SDSS ID: 1237665429707096375, reported by GCN\nCircular #31203). We performed forced photometry at the position of the\ncandidate against the nearby galaxy. The magnitudes and the 5-sigma limits\nof the stacked images are as follows.\n\nT0+[hour] | MID-UT | T-EXP[sec] | candidate magnitude | 5-sigma limits\n------------------------------------------------------------------------------------------------\n6.3 | 2021-12-11 19:25:34 | 6600 | g'=20.4 +/- 0.2, Rc=20.3 +/- 0.1,\nIc=20.4 +/- 0.3 | g'>20.2, Rc>20.7, Ic>19.7\n------------------------------------------------------------------------------------------------\nT0+ : Elapsed time after the burst\nT-EXP: Total Exposure time\n\nWe used id 141492123232234127 of PS1 catalog for flux calibration. The\nconversion from PS1 r and i band to our Rc and Ic band is by the equation\nof Tonry et al. (2012), Table. 6. The magnitudes are expressed in the AB\nsystem. The images were processed in real-time through the MITSuME GPU\nreduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24;\nhttps://github.com/MNiwano/Eclaire).",
  "circularId": 31217,
  "createdOn": 1639315100000,
  "email": "n.ito@hp.phys.titech.ac.jp",
  "subject": "GRB 211211A: MITSuME Akeno optical observation",
  "submitter": "Naohiro Ito at Tokyo Tech  <n.ito@hp.phys.titech.ac.jp>",
  "eventId": "GRB 211211A"
}