{
  "bibcode": "2012GCN.13328....1R",
  "body": "A. Rossi (TLS Tautenburg), M. Nardini (Universita'degli Studi \nMilano-Bicocca), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching) \nreport on behalf of the GROND team:\n\nWe observed the field of GRB 120521B (Swift trigger 522586; Cummings et \nal., GCN 13305) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al. \n2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla \nObservatory (Chile).\n\nObservations started at 00:35 UT on 2012-05-22, 15.3 h after the GRB \ntrigger, and lasted for 140 minutes. They were performed with good sky \nconditions at an average seeing of 0.8\" and at an average airmass of 1.05. \n(At the time of the GRB trigger the field was already too close to the \ntelescope's horizon distance limit in order to observe it with GROND.)\n\nBased on an exposure of 37 minutes in the optical and 30 minutes in the \nNIR we do not detect any source within the Swift-XRT error circle reported \nby Osborne et al. (GCN 13311). Preliminary observed upper limits (AB mags) \nare:\n\n  g' > 24.5\n  r' > 24.2\n  i' > 23.9\n  z' > 23.9\n  J  > 21.3\n  H  > 20.3\n  Ks > 19.3.\n\nThese limits are derived based on GROND zeropoints (g'r'i'z') and 2MASS \nstars (JHK). We note that the Galactic reddening along the line of sight \nis E_(B-V)= 0.45 mag (Schlegel et al. 1998).",
  "circularId": 13328,
  "createdOn": 1337675085000,
  "email": "klose@tls-tautenburg.de",
  "subject": "GRB 120521B: GROND Upper limits",
  "submitter": "Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>",
  "eventId": "GRB 120521B"
}