K. Wiersema, N. Tanvir (Leicester), A. Levan (Warwick), D. Malesani (DARK,
NBI), P. Jakobsson (Hertfordshire), E. Rol and R. Starling (Leicester)
report on behalf of a larger collaboration:
We observed the BAT position of the short GRB 071112B (GCN 7071) using
FORS2 on the VLT. We acquired two epochs of data, the first in VRI, the
second in R band only. The first R band epoch, consisting of 5 x 4 minutes
exposures, started at 00:25:02 UT on 13 november. The second epoch, again
5 x 4 minutes exposures, started at 00:47:00 UT on 14 november. Both
epochs were taken in good seeing conditions (0.7 and 0.9 arcsec
respectively) but at high airmass. Limiting magnitudes (3 sigma) are
estimated at R = 25.2 and R = 25.5 for the first and second epochs,
Both visual inspection and PSF-matched image subtraction using the ISIS2
code (Alard 2000) did not reveal a significantly fading source in or near
the BAT error circle.
We note that the limiting magnitudes above may not be fully representative
for the upper limit on the afterglow brightness, as the BAT error circle
contains some nebulosity, and the dithering pattern employed to avoid the
chip-gap between the two FORS2 chips means that a narrow strip through the
error circle has received comparatively less illumination.
We thank the Paranal staff for their excellent support, particularly
Stephane Brillant and Linda Schmidtobreick.