{
  "bibcode": "2017GCN.21910....1G",
  "body": "C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), \nA. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), A. Cucchiara, D. Morris, \nand B. Gendre (U. Virgin Islands) on behalf of a large collaboration report:\n\nWe began observing Swift GRB 170921A (D'Ai et al. GCN 21901) on \nSeptember 21, from 14:52 to 15:05 UT (from 24 to 37 minutes since the \nGRB trigger time) with the LCO 2-m telescope in Hawaii in the SDSS R and \nI filters. Within the enhanced Swift-XRT circle (Beardmore et al. GCN \n21906) we do not detect any optical counterpart down to the following \nlimits, in agreement with previous reports (Klotz et al. GCN 21903; \nKuroda et al. GCN 21905; Feng et al. GCN 21907; Malesani et al. GCN 21909):\n\nMid Time����� Exposure������ Filter������ Magnitude (AB)\n(min)���������� (s)\n-------------------------------------------------------\n26.8���������� 5x60��������� SDSS-R������� > 20.7\n34.0���������� 3x60��������� SDSS-I������� > 19.8\n-------------------------------------------------------\n\nas calibrated against nearby SDSS objects.",
  "circularId": 21910,
  "createdOn": 1506082053000,
  "email": "guidorzi@fe.infn.it",
  "subject": "GRB 170921A: LCO 2m telescope observations",
  "submitter": "Cristiano Guidorzi at Ferrara U,Italy  <guidorzi@fe.infn.it>",
  "eventId": "GRB 170921A"
}