TITLE:   GCN CIRCULAR
NUMBER:  19142
SUBJECT: GRB 160303A: VLT/FORS2 afterglow obervations
DATE:    16/03/04 15:36:10 GMT
FROM:    Thomas Kruehler at MPE Garching  <kruehler@mpe.mpg.de>

S. Klose, A. Nicuesa Guelbenzu (both TLS Tautenburg),
T. Kruehler (MPE Garching), D. Malesani (DARK/NBI) and J. Greiner
(MPE Garching) report on behalf of a larger collaboration:

We observed the field of GRB 160303A (Swift trigger 677495; Beardmore et
al., GCN #19126) with FORS2 at ESO's Very Large Telescope. Imaging in
the R-band filter started at 05:40:42 UT on 2016-03-04, 18.8 hr after
the GRB trigger.

In a 4x25 s exposure, we clearly detect the candidate counterpart
(Butler et al. GCN#19131, Emery & Beardmore, GCN#19134,
de Ugarte Postigo et al. GCN#19136) at a position consistent with
the one provided by de Ugarte Postigo et al. (GCN#19136). The source
appears point-like in the image which has a stellar PSF with a
FWHM of 0.72".

Calibrating our data against r-band photometry of field stars
from the SDSS catalog, we measure a preliminary AB magnitude of

r = 24.11 +- 0.15

This implies significant fading against the earlier measurements from
Butler et al. (GCN#19131) and de Ugarte Postigo et al. (GCN#19136),
indicating that this source is the GRB afterglow (see also Im et al., 
GCN#19141).

We acknowledge excellent support from ESO Paranal Science Operations,
in particular from Emanuela Pompei and the team at VLT/Antu.

[GCN OPS NOTE(06mar16): Per author's request, the final paragraph was added.]