GCN Circular 29806
Subject
GRB 210411C: VLT/X-shooter redshift
Date
2021-04-12T10:46:55Z (3 years ago)
From
Daniele B Malesani at DTU Space <malesani@space.dtu.dk>
A. de Ugarte Postigo (HETH/IAA-CSIC and DARK/NBI), B. Sbarufatti (PSU),
D. Xu (NAO/CAS), J.-B. Vielfaure (APC, Paris University), D. B. Malesani
(DTU Space), D. A. Kann (HETH/IAA-CSIC) V. D'Elia (ASI/SSDC, INAF/OAR),
P. J. Pessi (FCAG/ESO), report on behalf of the Stargate consortium:
We observed the optical afterglow of GRB 210411C (Sbarrato et al., GCN
29794) using the ESO VLT UT3 (Melipal) equipped with the X-shooter
spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and
consist of 4 exposures by 1200 s each (8x600 s in the NIR). The
observation mid time was 2021 Apr 12.33 UT (16.9 hr after the GRB).
In a 60 s image taken with the acquisition camera on Apr 12.294 UT, we
detect the optical afterglow, for which we measure an AB magnitude r =
21.69 +- 0.04 (calibrated against nearby stars from the SkyMapper
catalog; Wolf et al. 2018, PASA, 35, 010;
https:doi.org/10.4225/41/593620ad5b574).
We clearly detect continuum over the wavelength range 3520 - 17500 AA. A
trough is visible around 4650 AA, which we identify as due to H I. From
the detection of several narrow absorption features, which we interpret
as due to, among others, Si II, Si II*, O I, C II, Si IV, C IV, Fe II,
Al II, we infer a redshift z = 2.826. We also identify the FeII* 2396
fine-structure transition, though at low S/N.
We acknowledge excellent support from the observing staff at Paranal, in
particular Eleonora Sani and Bin Yang.
[GCN OPS NOTE(12apr2021): Per author's request, GRB in the SUBJECT line
was changed from 210411A" to the correct name "210411C".]