TITLE:   GCN CIRCULAR
NUMBER:  9408
SUBJECT: GRB 090519: GROND observation
DATE:    09/05/20 08:02:04 GMT
FROM:    Jochen Greiner at MPI  <jcg@mpe.mpg.de>

A. Rossi (Tautenburg), T. Kruehler, J. Greiner and A. Yoldas (all MPE Garching)
report on behalf of the GROND team:

We observed the field of GRB 090519 (Swift trigger 352648, M. Perri et al.,
GCN #9400) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m
ESO/MPI telescope at La Silla Observatory (Chile). Observations started on
19 May 2009 at 23:44 UT, 2.5 h after the burst, under challenging sky 
conditions with cirrus.

We detect the afterglow at a position consistent with the enhanced XRT error 
circle and NOT (Thoene et al., GCN #9403). With an exposure time of 40min in 
JHK and 49min in griz, preliminary photometry yields the following AB 
magnitudes:
 
g =25.0 +-0.4
r =23.5 +-0.2
i =23.5 +-0.3
z >23.6
J >21.9
H >20.7
K >19.9

calibrated using SDSS and 2MASS field stars. The quoted magnitudes are not 
corrected for the galactic foreground extinction corresponding to a 
reddening of E_(B-V)=0.04.

The large g-i color as compared to r-i indicates that the Lyman break may
be located in the g' band. Fitting the SED with Hyper-Z results in a 
preliminary photometric redshift of z = 3.9+0.4-0.7, assuming no intrinsic 
extinction.