{
  "bibcode": "2015GCN.18317....1Y",
  "body": "R. Yates, J. Bolmer and J. Greiner (all MPE Garching) report on behalf of\nthe GROND team:\n\nWe observed the field of GRB 150915A (D'Elia et al., GCN 18315) simultaneously\nin g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at \nthe 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations \nstarted at 23:28 UT on 2015-09-15, 2.2 hours after the GRB trigger.\n\nBased on a 42 minutes exposure at a mid-time of 3.7 hours after the BAT \ntrigger, at an average seeing of 1.6\" and at an average airmass of 1.0, \nwe detect an optical counterpart at the edge of the Swift-XRT error-circle at\n  RA = 21 18 37.84\n  Decl. = -34 54 48.3\n(+/- 0.3\")\n\nat the following with magnitudes (AB system)\n\ng' = 23.0 +/- 0.1 mag,\nr' = 23.1 +/- 0.1 mag,\ni' = 22.9 +/- 0.2 mag,\nz' = 22.7 +/- 0.2 mag,\nJ  > 19.9 mag,\nH  > 19.3 mag,\nK  > 17.9 mag.\n\nThe given magnitudes are derived based on calibrating the images against\nGROND zeropoints in the optical and 2MASS in the NIR, and are not corrected \nfor the expected Galactic foreground extinction corresponding to a reddening \nof E_(B-V) = 0.10 mag in the direction of the burst (Schlegel et al. 1998).",
  "circularId": 18317,
  "createdOn": 1442385648000,
  "email": "jcg@mpe.mpg.de",
  "subject": "GRB 150915A: GROND detection of an optical counterpart candidate",
  "submitter": "Jochen Greiner at MPI  <jcg@mpe.mpg.de>",
  "eventId": "GRB 150915A"
}