{
  "bibcode": "2017GCN.21200....1S",
  "body": "P. Schady (MPE) reports:\n\nWe observed the field of GRB 170604A (Swift trigger 755867; Page et al.,\nGCN #21191) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,\nPASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla\nObservatory (Chile).\n\nObservations started at 06:15 UT on 05-06-2017, 11.1 hours the GRB\ntrigger. They were performed at an average seeing of 1.3\" and at an\naverage airmass\nof 2.\n\nWe detect a point source within the 1.4\" enhanced Swift/XRT error circle\n(Page et al., GCN 21196), and consistent with the afterglow position\nreported by Izzo et al. (GCN #21192).\n\nBased on a total exposure of 4.6 min in g'r'i'z' and 4 min in JHK, we\nestimate preliminary magnitudes (all in AB) of\n\ng' = 20.75 +/- 0.08\nr' = 20.46 +/- 0.05\ni' = 20.35 +/- 0.06\nz' = 20.21 +/- 0.08\nJ = 19.6 +/- 0.1\nH = 19.6 +/- 0.3\nK > 19.6\n\nGiven magnitudes are calibrated against PanSTARRS and 2MASS field stars\nand are not corrected for the expected Galactic foreground extinction\ncorresponding to a reddening of E_(B-V)=0.03 mag in the direction of the\nburst (Schlafly & Finkbeiner 2011).\n\nWe acknowledge the excellent support provided by Simona Ciceri in\nobtaining these data.",
  "circularId": 21200,
  "createdOn": 1496661622000,
  "email": "pschady@mpe.mpg.de",
  "subject": "GROND observations of GRB170604A",
  "submitter": "Patricia Schady at MPE/Swift  <pschady@mpe.mpg.de>",
  "eventId": "GRB 170604A"
}