GCN Circular 23114
Subject
GRB 180809B: VLT optical upper limits
Date
2018-08-10T10:18:56Z (6 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
J. Japelj (U. Amsterdam), D. B. Malesani (DAWN/NBI and DARK/NBI), J.
Selsing (DAWN/NBI), N. R. Tanvir (U. Leicester), D. A. Kann
(HETH/IAA-CSIC), V. D'Elia (ASI-SSDC), G. Pugliese (U. Amsterdam), K. E.
Heintz (Univ. Iceland and DAWN/NBI), J. P. U. Fynbo (DAWN/NBI), A. J.
Levan (Univ. Warwick), P. Schady (University of Bath), report on behalf
of the Stargate collaboration:
We observed the field of GRB 180809B with the ESO VLT UT2 (Kueyen),
using the X-shooter acquisition camera. In a single 120-s r-band
exposure, with a mean epoch Aug 10.055 UT (4.84 hr after the GRB), we
detect no object at the position of the optical afterglow (e.g., Moss et
al., GCN 23105; Lipunov et al., GCN 23109; Schweyer et al. GCN 23111;
Guidorzi et al., GCN 23112, Tiurina et al., GCN 23113), down to a
limiting magnitude r > 24.7 AB (calibrated against nearby Pan-STARRS
sources).
Compared to the r-band measurement by Guidorzi et al. (GCN 23112), and
assuming an unbroken power-law decay F(t) propto t^-alpha, the
corresponding decay index is alpha > 2.2 between 0.55 and 4.84 hr after
the GRB.
We acknowledge excellent support from the observing team in Paranal,
including Steffen Mieske and Boris Haeussler.