GRB 191221B: VLT/X-shooter redshift
Abstract
We observed the optical afterglow of GRB 191221B (Laha et al., GCN 26534; Longo et al., GCN 26549; Lipunov et al., GCN 26537). using the ESO VLT UT2 (Kueyen) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 2 exposures by 600 s each. The observation mid time was 2019 Dec 22.2707 UT (9.843 hr after the GRB). In a 15 s image taken with the acquisition camera on Dec 22.2592 UT, we detect the optical afterglow, for which we measure a magnitude r = 17.13 +- 0.01 AB (calibrated against nearby stars from the Skymapper catalog; Wolf et al. 2018, PASA, 35, 010; https:doi.org/10.4225/41/593620ad5b574). We detect several absorption profiles in the GRB spectrum including MgII, MgI, SiII, CIV, AlII, NiII, and FeII lines. From these metal lines we infer a redshift z=1.148 for the GRB, consistent with the redshift reported by Swift/UVOT tram (GCN 26538). We also detect the MgII absorption profile corresponding to an intervening system at z=0.961. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Pascale Hibon, Francisco Belmar, and Trystyn Berg.
- Publication:
-
GRB Coordinates Network
- Pub Date:
- December 2019
- Bibcode:
- 2019GCN.26553....1V