{
  "bibcode": "2015GCN.18507....1W",
  "body": "P. Wiseman, J. Greiner (both MPE Garching) report on behalf of the GROND\nteam:\n\nWe observed the field of GRB 151027B (Swift trigger 661869; (Ukwatta et\nal., GCN 18499) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.\n2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla\nObservatory (Chile).\n\nObservations started at 06:24 UT on 28/10/2015, 7 hrs 45 mins after the\nGRB trigger, and are continuing. They were performed at an average seeing\nof 0.9\" and at an average airmass of 1.1.\n\nWe found a single point source within the enhanced 1.8\" Swift-XRT error\ncircle reported by Evans et al. (GCN 18504), common with that reported by\nMalesani et al. (GCN 18501) and Xu et al. (GCN 18505).\n\nBased on 6.6 min of total exposures in g'r'i'z'JHK at a mid time of\n06:33:39 UT, we estimate preliminary magnitudes (all in AB system) of\n\ng' > 22.4 mag,\nr' = 20.8 +/- 0.08 mag,\ni' = 20.1 +/- 0.07 mag,\nz' = 20.1 +/- 0.07 mag,\nJ = 20.1 +/- 0.4 mag,\nH = 19.1 +/- 0.3 mag, and\nK > 18.3 mag.\n\nA clear g'-band drop out in the SED leads to a photo-z of 4.3 + 0.3,-0.2,\nconsistent with the redshift derived from the X-shooter spectrum (Xu et\nal., GCN 18505). The source appears to be fading relative to the NOT\nreport (Malesani et al., GCN 18501), and has continued to do so during our\nobservations.\n\nGiven magnitudes are calibrated against GROND zeropoints (g'r'i'z') as\nwell as 2MASS field stars (JHK) and are not corrected for the expected\nGalactic foreground extinction corresponding to a reddening of E_(B-V)=0.2\nmag in the direction of the burst (Schlegel et al. 1998).",
  "circularId": 18507,
  "createdOn": 1446018047000,
  "email": "wiseman@mpe.mpg.de",
  "subject": "GRB 151027B: GROND Optical/NIR Afterglow Detection",
  "submitter": "Philip Wiseman at MPE/Swift  <wiseman@mpe.mpg.de>",
  "eventId": "GRB 151027B"
}