{
  "bibcode": "2018GCN.23111....1S",
  "body": "Tassilo Schweyer (MPE Garching) and Patricia Schady (University of Bath) report:\n\nWe observed the field of GRB 180809B (Swift trigger 852553; Moss et al., GCN #23105) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).\n\nObservations started at  23:00UT on 2018-08-09, 2.5 hrs after the GRB trigger. They were performed at an average seeing of 1.3\" and at an average airmass of 2.\n\nWe detect a source in the JHK bands consistent with the position of the X-ray and optical afterglow (Mass et al., GCN #23105; Lipunov et al., GCN #23109). Based on a total exposure of time of 19 minutes in g'r'i'z' and 29 minutes in JHK we estimate the following AB magnitudes and upper limits at the position of the UVOT detection:\n\ng' > 23.9 mag\nr' > 23.9 mag\ni' > 22.9 mag\nz' > 22.4 mag\nJ = 21.0 +/- 0.3 mag\nH = 19.9 +/- 0.2 mag\nK = 18.7 +/- 0.1 mag\n\nGiven magnitudes are calibrated against PanSTARRS and 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.14 in the direction of the burst (Schlafly & Finkbeiner 2011).\n\nWe thank Markus Rabus for the excellent support from La Silla.",
  "circularId": 23111,
  "createdOn": 1533885550000,
  "email": "p.schady@bath.ac.uk",
  "subject": "GRB 180809B: GROND Detection of the NIR Afterglow",
  "submitter": "Patricia Schady at Swift  <p.schady@bath.ac.uk>",
  "eventId": "GRB 180809B"
}