{
  "bibcode": "2021GCN.29825....1P",
  "body": "Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Chung-Uk Lee\n(KASI), Seung-Lee Kim (KASI), Hyun-Il Sung (KASI) on behalf of a larger\ncollaboration\n\nWe searched for the optical counterpart of GRB 210413B (A. Tohuvavohu et\nal. GCN #29819, and P. A. Evans et al., GCN #29821) with the 1-m class\ntelescope in Lemonsan Optical Astronomy Observatory (LOAO), one of\nfacilities of the GW EM-Counterpart Korean Observatory (GECKO).\n\nWe observed the center of Swift/BAT localization (RA, Dec = 182.558 +55.965),\nbut could not find any transient within the field of view of LOAO\n(28.1'x28.1'). We calibrated flux with the PS1 catalog and used an AB\nmagnitude system.\n\n------\nFilter Date-obs[UT] Exp.time[s] Depth(5sigma)\nB 2021-04-16T03:17:51.667 180*3 20.780\nV 2021-04-16T03:27:54.933 180*3 20.347\nR 2021-04-16T03:37:58.867 180*3 19.594\nI 2021-04-16T03:47:55.800 180*3 19.293\n\nWe thank the LOAO opertator for performing the observation.\nGravitational-wave EM Counterpart Korean Observatory (GECKO) is a network\nof 10+ 0.5m to 1m class telescopes over the world.",
  "circularId": 29825,
  "createdOn": 1618641928000,
  "email": "shpaek@astro.snu.ac.kr",
  "subject": "GRB 210413B: LOAO optical upper limit",
  "submitter": "Gregory SungHak Paek at SNU  <shpaek@astro.snu.ac.kr>",
  "eventId": "GRB 210413B"
}