[vsnet-grb-info 7411] GRB 090309A: GROND upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8975
SUBJECT: GRB 090309A: GROND upper limits
DATE:    09/03/11 00:24:38 GMT
FROM:    Adria C. Updike at Clemson U  <aupdike at clemson.edu>

A. C. Updike (Clemson University), C. Clemens, and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of the possibly short/hard GRB 090309 (Swift trigger
345945; Evans et al., GCN #8964) 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 07:22 UT on March 10th, 7.9 hours after the GRB
trigger and continued for 2.5 hours at an average seeing of 1.5" and an
average airmass of 1.5.

In one hour of stacked exposures, we do not detect a source within the
Swift-XRT enhanced error circle (Goad et al., GCN #8969) down to

g' > 23.4,

r' > 23.8,

i' > 23.2,

z' > 23.0,

J > 21.3,

H > 21.0 and

K > 20.3

The given limits in the AB system are derived based on calibrating the
images against GROND zeropoints and 2MASS field stars and are not
corrected for the Galactic foreground extinction corresponding to a
reddening of E_(B-V)= 0.23 in the direction of the burst (Schlegel et al.
1998).