TITLE:   GCN CIRCULAR
NUMBER:  10091
SUBJECT: GRB 091026: GROND Upper Limits
DATE:    09/10/27 05:38:20 GMT
FROM:    Adria C. Updike at Clemson U  <aupdike@clemson.edu>

Robert Filgas (Tautenburg Obs.), Adria Updike (Clemson University), Arne
Rau, and Jochen Greiner (both MPE Garching) report on behalf of the GROND
team:

We observed the field of GRB 091026 (Swift trigger 373871; Markwardt et
al., GCN #10081) 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 00:48 UT on Oct 27, 2009, 11.6 hours after the GRB
trigger.  They were performed at an average seeing of 2" and at an average
airmass of 1.94.

We do not detect a source within the Swift-XRT error circle reported by
Evans et al. (GCN #10084) down to

g' > 24.8 mag,

r' > 24.2 mag,

i' > 23.9 mag,

z' > 23.7 mag,

J > 22.2 mag,

H > 21.3 mag and

K > 20.2 mag.

Magnitudes are given in the AB system and calibrated against USNO as well
as 2MASS field stars, and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V) = 0.13 mag
in the direction of the burst (Schlegel et al. 1998).