GCN Circular 29685
Subject
GRB 210321A: Redshift from OSIRIS/GTC
Event
Date
2021-03-21T22:57:51Z (5 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D.A. Kann,
C. Thoene, M. Blazek, J.F. Agui Fernandez (all HETH/IAA-CSIC),
S. Geier (GTC, IAC), A. Tejero (GTC) report:
We observed the afterglow of GRB 210321A (Dichiara et al. GCN
29677; Perri et al. GCN 29678; Siegel et al. GCN 29679; Butler et
al. GCN 29680; Heintz et al. GCN 29684) with OSIRIS at the
10.4m GTC telescope at Roque de los Muchachos Observatory,
in La Palma (Spain). The observation started at 20:28 UT (0.5517
days after the burst), and consisted in 3x900s with grism R1000B,
covering the spectral range from 3700 to 7800 AA.
The 30s acquisition image, with a seeing of 0.75���, shows the
afterglow at a magnitude of r��� = 21.39+/-0.03, using a nearby
PanSTARRS field star as photometric reference.
The spectral continuum is well detected above 3900 AA, and
shows very weak lines consistent with several features of FeII, MgII
and MgI at a common redshift of z = 1.487, which we assume to be
the likely redshift of the GRB. However, we note that strictly
speaking this would be a lower limit, with the upper limit being z ~< 2,
as already noted by the NOT spectroscopy (Heintz et al. GCN 29684).