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GCN Circular 19142

GRB 160303A: VLT/FORS2 afterglow obervations
2016-03-04T15:36:10Z (8 years ago)
Thomas Kruehler at MPE Garching <>
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., 

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.]
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