GCN Circular 9245
Subject
GRB 090424: GROND Observations of the Optical/NIR Afterglow
Event
Date
2009-04-25T04:34:34Z (17 years ago)
From
Aybuke Kupcu Yoldas at ESO <ayoldas@eso.org>
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.