GCN Circular 29717
Subject
Short GRB 210323A: GTC Observations
Date
2021-03-24T19:49:17Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann
(HETH/IAA-CSIC), D. B. Malesani (DTU Space), N. R. Tanvir (Univ.
Leicester), C. Thoene, M. Blazek, J. F. Agui Fernandez (all
HETH/IAA-CSIC), and S. Geier (GTC, IAC) report:
We observed the afterglow (Malesani et al., GCN #29703, Pozanenko et
al., GCN #29708) of the short/hard GRB 210323A (Swift detection: Gropp
et al., GCN #29699, Fermi GBM detection: Hamburg & Meegan, GCN #29709;
Konus-Wind detection: Frederiks et al., GCN #29713) with OSIRIS at the
10.4m GTC telescope at Roque de los Muchachos Observatory, in La Palma
(Spain). The observation started at 05:31 UT (0.3118 days after the
burst), and consisted of 3 x 600s with grism R1000B, covering the
spectral range from 3700 to 7800 AA. Observations were taken at high
airmass, near dawn.
The 60 s acquisition image, with a seeing of 1".3, shows the afterglow
at a magnitude of r' = 23.03 +/- 0.15 mag, using a nearby Pan-STARRS
field star as photometric reference. This is in agreement with the NOT
measurement.
Spectral continuum is faintly detected above 5000 AA, and shows no clear
evidence for any absorption or emission lines. We therefore place a weak
upper limit of z < 3.1 on the redshift of GRB 210323A. There may be
evidence for a low-significance emission line at 5110 AA, which is
slightly offset from the continuum trace in the 2D spectrum. It is found
using multiple reductions and analyses. Interpreting this line as [OII],
the corresponding redshift would be z = 0.37. However, we do not find
any evidence for other emission lines, such as Hbeta and [OIII], at the
corresponding redshift, placing its reality in doubt.
Further observations will be required to verify the reality of this
feature and to attempt a redshift determination through host galaxy
spectroscopy.