GCN Circular 13328

A. Rossi (TLS Tautenburg), M. Nardini (Universita'degli Studi 
Milano-Bicocca), S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching) 
report on behalf of the GROND team:

We observed the field of GRB 120521B (Swift trigger 522586; Cummings et 
al., GCN 13305
Not found
 
 
) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al. 
2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla 
Observatory (Chile).

Observations started at 00:35 UT on 2012-05-22, 15.3 h after the GRB 
trigger, and lasted for 140 minutes. They were performed with good sky 
conditions at an average seeing of 0.8" and at an average airmass of 1.05. 
(At the time of the GRB trigger the field was already too close to the 
telescope's horizon distance limit in order to observe it with GROND.)

Based on an exposure of 37 minutes in the optical and 30 minutes in the 
NIR we do not detect any source within the Swift-XRT error circle reported 
by Osborne et al. (GCN 13311
Not found
 
 
). Preliminary observed upper limits (AB mags) 
are:

  g' > 24.5
  r' > 24.2
  i' > 23.9
  z' > 23.9
  J  > 21.3
  H  > 20.3
  Ks > 19.3.

These limits are derived based on GROND zeropoints (g'r'i'z') and 2MASS 
stars (JHK). We note that the Galactic reddening along the line of sight 
is E_(B-V)= 0.45 mag (Schlegel et al. 1998).