GCN Circular 20004
Subject
GRB 160927A: GTC observations
Date
2016-10-06T15:58:07Z (8 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), L. Izzo (IAA-CSIC),
D.A. Kann (TLS Tautenburg), C.C. Thoene (IAA-CSIC), Z. Cano
(IAA-CSIC), D. Reverte-Paya (GRANTECAN, IAC, ULL) report on
behalf of a larger collaboration:
We observed the afterglow of the short-hard GRB 160927A (Gibson
et al., GCN 19952) with OSIRIS on the 10.4m GTC telescope.
Observations consisted in 10x190s exposures in r-band, with a mean
epoch on 28 September 2016 at 20:26 UT (26.52 hr after the burst).
The optical counterpart (Tkachenko et al., GCN 19954; D���Avanzo et
al., GCN 19956; Wiseman et al. GCN 1959; Xu et al., GCN 19960;
Fong et al., GCN 19964) is detected at a magnitude of r_AB =
25.3+/-0.2, as compared to several SDSS field stars.
Combining this observation with the rest of the available GCN data,
the light curve indicates an early evolution with a shallow decay,
followed by a faster decay (as already mentioned by Wiseman et al.
GCN 1959 and Xu et al., GCN 19960), with the break at around the
TNG epoch, after which we estimate a decay rate of with alpha =
-1.03+/-0.08 (where F~t^alpha).This decay is significantly shallower
than the one reported by (Xu et al., GCN 19960), indicating that the
light curve may be flattening at the time of the GTC observation. This
could be due to the contribution of an additional component (either
the host galaxy, or more unlikely the contribution of a kilonova) or just
due to the uncertainties of the different photometric measurements.