GCN Circular 9268
Subject
GRB 090426: GROND Observations of the Optical/NIR Afterglow
Event
Date
2009-04-27T03:28:00Z (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 350479; Cummings et
al., GCN #9254) 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 01:08 UT on 27 April, ~12.5 hours after the GRB
trigger, and are continuing. They are performed at an average seeing of
1.2 and at an average airmass of 2.5.
We clearly detect the optical/near-infrared afterglow (Cummings et al.
GCN #9254; Xin et al. #GCN 9255; Oates et al. GCN #9265; Yoshida et al.
GCN #9266, #9267) in all GROND bands.
Preliminary photometry yields the following AB magnitudes in stacked
images, obtained using SDSS/2MASS stars as reference:
Filter Exp[s] AB Mag MagErr
----------------------------------------
g' 4x115 22.04 0.03
r' 4x115 21.24 0.24
i' 4x115 21.77 0.11
z' 4x115 21.43 0.09
J 48x10 20.40 0.10
H 48x10 20.09 0.12
K 48x10 19.83 0.17
Given magnitudes are not corrected for the expected Galactic foreground
extinction corresponding of E_(B-V)=0.02 mag (Schlegel et al. 1998).
Using these magnitudes combined with the results of previous
observations (Yoshida et al. GCN #9266) we estimate a simple power law
decay with an index of ~0.86.