[vsnet-grb-info 5427] VLT FORS2 observations of short hard GRB071112B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7101
SUBJECT: VLT FORS2 observations of short hard GRB071112B
DATE:    07/11/17 18:36:03 GMT
FROM:    Rhaana Starling at U of Leicester  <rlcs1 at star.le.ac.uk>

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, 
respectively. 

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.