[vsnet-grb-info 9190] GRB 100424A: GROND Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10676
SUBJECT: GRB 100424A: GROND Upper Limits
DATE:    10/04/25 06:32:41 GMT
FROM:    Thomas Kruehler at MPE/MPI  <kruehler at mpe.mpg.de>

F. Olivares, T. Kruehler and J. Greiner (all MPE Garching) report on 
behalf of the GROND team:

We observed the field of GRB 100424A (Swift trigger 420367; Hoversten et 
al., GCN 10667) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 
2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla 
Observatory (Chile).

Observations started at 00:16 UT on April 25, 7.7 hours after the GRB 
trigger, and continued for 3 hours. The observations were severely 
affected by passing cirrus clouds.

In our first stacked images of 24 min total integration time in g'r'i'z' 
and 20 min in JHK, we do not (see also Malesani et al., GCN 10671, Levan 
et al., GCN 10672, Morgan & Bloom GCN 10675) detect a source within the 
enhanced Swift/XRT error circle (Evans et al., GCN 10669) down to the 
following preliminary 3 sigma limiting magnitudes (all in the AB system):

g' > 23.03
r' > 23.37
i' > 22.96
z' > 23.04
J > 21.77
H > 21.21
K > 20.29

Later images do not increase these limiting magnitudes due to worse sky 
conditions. These limits were derived by calibrating the images against 
SDSS/2MASS field stars and are not corrected for the Galactic foreground 
extinction corresponding to a reddening of E_(B-V)= 0.03 in the 
direction of the burst (Schlegel et al. 1998).