GCN Circular 19245
Subject
GRB 160327A: Imaging and spectroscopy from GTC
Date
2016-03-29T18:18:21Z (8 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), N.R. Tanvir (U. Leicester),
Z. Cano (U. Iceland), L. Izzo (U. Roma1), J.P.U. Fynbo (DARK/NBI),
R. Sanchez-Ramirez (IAA-CSIC), C.C. Thoene (IAA-CSIC), P. Pesev
(GRANTECAN, IAC, ULL) report:
We observed the field of GRB 160327A (Racusin, et al., GCN 19235) with
OSIRIS mounted on the 10.4 m GTC telescope, located at Roque de los
Muchachos Observatory (La Palma, Spain) starting at 00:26 UT on 28th
March 2016 (15.17 hr after the burst).
In the acquisition image, we identify the afterglow proposed by Golkhou
et al. (GCN 19236) and later also observed by Zheng & Filippenko (GCN
19242). At the time of our observation, the object was at a magnitude
of i(AB) = 23.89 +/-0.12 (as compared to nearby SDSS stars), with
coordinates of (J2000.0, +/-0.5"):
R.A.: 09:46:48.56
Dec.: +54:00:46.3
We also note the presence of two other sources within 2.5��� of the GRB
afterglow: The first one is located at 09:46:48.35, +54:00:47.8 and has a
magnitude of i(AB) = 23.76+/-0.11, and the second one is at 09:46:48.55,
+54:00:44.2 with a magnitude of i(AB) = 24.24+/-0.15. We suspect that
these sources may be contributing to the magnitudes given by Golkhou
et al. (GCN 19243), especially in the bluer bands.
Spectroscopy of the GRB afterglow and the first of the two other objects
was obtained by exposing 3x1200 s with grism R1000R, which covers
between 5100 and 10100 Angstrom. We detect a trace of the GRB
afterglow above 7300 AA, below which the emission drops abruptly. The
other object shows a continuum over the complete spectral range,
suggesting that this object is unrelated to the GRB. The afterglow
spectrum is indicative of a Lyman-alpha drop at a redshift between 4.90
and 5.01, with a most probable value at z = 4.99, although even lower
redshifts could not be discarded for unusually large Hydrogen column
densities. Due to the low S/N of the spectrum we are not able to confirm
any other absorption lines at this time.