{
  "bibcode": "2007GCN..6449....1G",
  "body": "J. Greiner, C. Clemens, T. Kruehler, A. Kuepcue-Yoldas, N. Primak, \nG. Szokoly, A. Yoldas (all MPE Garching), S. Klose, U. Laux (Tautenburg Obs), \nand C.C. Thoene (DARK/NBI Copenhagen) report:\n\nWe have observed GRB 070521 (trigger 279935, Guidorzi et al. 2007, \nGCN #6431) with the 7-channel imager GROND, mounted at the \n2.2m Max-Planck Institute telescope at La Silla (ESO/Chile). Observations \nstarted at 06:59 UT, about 8 min. after the GRB trigger, and continued \nfor 25 min until the telescope's elevation limit of 20 deg above horizon \nwas reached. The observation consisted of a series of 60-second\nexposures each in g', r', i, and z', and 10-second exposures in J, H, \nand Ks, respectively. The GRB field was observed through changing,\nthick cloud coverage, therefore, only 50% of the images are useful and \nthe flux in the remaining images is reduced.\n\nNo source is detected within the Swift XRT error circle (GCN #6431).\nWe derive the following, preliminary 2 sigma upper limits using\nSDSS (Cool et al 2007, GCN #6432) and 2MASS photometry of stars within\nthe field: \n   g' > 22.0 \n   r' > 21.7 \n   i  > 20.7 \n   z' > 20.3\n   J  > 20.0 \n   H  > 17.9 \n   K  > 17.2\n\nThe object see by Subaru (Hattori et al, GCN #6444) is not seen\nin any of our stacked images.\n\nGROND is presently being commissioned.",
  "circularId": 6449,
  "createdOn": 1179803120000,
  "email": "jcg@mpe.mpg.de",
  "subject": "GROND upper limits of GRB 070521",
  "submitter": "Jochen Greiner at MPI  <jcg@mpe.mpg.de>",
  "eventId": "GRB 070521"
}