GCN Circular 9245

F. Olivares (MPE Garching), A. Kupcu Yoldas (ESO), J. Greiner, A. Yoldas 
(both MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 090424 (Swift trigger 350311;Cannizzo et 
al., GCN #9223) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 
2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla 
Observatory (Chile).

Observations started at 02:52 UT on 25 April, ~12.5 hours after the GRB 
trigger, and are continuing. They were performed at an average seeing of 
1.0 and at an average airmass of 1.45.

We clearly detect the optical afterglow (Cannizzo et al. GCN #9223; Yuan 
et al. GCN #9224; Xin et al. GCN #9225; Schady et al. #9234; Gorosabel 
et al. GCN #9236).

Preliminary photometry yields the following AB magnitudes in stacked 
images of the first OB,  obtained using SDSS/2MASS stars as reference:

Filter  Exp[s]  AB Mag  MagErr
----------------------------------------
g'      4x115	20.98	0.02
r'      4x115	20.42	0.04
i'      4x115	20.01	0.04
z'      4x115	19.64	0.02
J 	48x10	19.08	0.09
H 	48x10	18.62	0.03
K 	48x10	18.29	0.04

Given magnitudes are not corrected for the expected Galactic foreground 
extinction corresponding of E_(B-V)=0.03 mag (Schlegel et al. 1998).
These magnitudes combined with the results of previous observations 
(Schady et al. GCN #9234, Guidorzi et al. GCN #9238) indicate a 
flattening in the afterglow light-curve.