{
  "bibcode": "2015GCN.18158....1D",
  "body": "S. Dichiara, C. Guidorzi (U. Ferrara), C.G. Mundell (U. Bath),\nS. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of\na large collaboration report:\n\nThe 1-m telescopes in Cerro Tololo (Chile) and McDonald (Texas)\n began observing Swift GRB 150817A (V. D'Elia, et al., GCN 18143).\non August 17 at 03:16:31 UT, i.e. ~70 minutes since the BAT trigger,\nwith the r' and i' filters. Further observations with the i' filter\nwere performed using the 2-m Faulkes Telescope North ~400 min after\nthe trigger.\n\nWithin the enhanced XRT error circle (Osborne et al. GCN Circ. 18146)\nwe find no optical counterpart to the following limiting magnitude:\n\nMid time from  Total Exp   Filter    Magnitude\ntrigger (min)   (s)\n-------------------------------------------------\n75.9         120x9       r'        > 19.6\n86.3         120x8       i'        > 18.5\n107.6        120x5       r'        > 19.7\n119.2        120x5       i'        > 19.1\n408.1        120x5       i'        > 20.7\n-------------------------------------------------\n\nOur results are consistent with the previous observations reported by\nButler et al. (GCN Circ. 18144) and Cenko et al. (GCN Circ. 18153).\n\nMagnitudes are calibrated against nearby USNO-B1 stars (R2 and I).",
  "circularId": 18158,
  "createdOn": 1439921016000,
  "email": "dichiara@fe.infn.it",
  "subject": "GRB 150817A: LCOGT observations",
  "submitter": "Simone Dichiara at Ferrara U/Italy  <dichiara@fe.infn.it>",
  "eventId": "GRB 150817A"
}