[vsnet-grb-info 23693] GRB 190919B: VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25792
SUBJECT: GRB 190919B: VLT/X-shooter redshift
DATE:    19/09/20 08:30:58 GMT
FROM:    Daniele B Malesani at DTU Space  <malesani at space.dtu.dk>

G. Pugliese (Univ. Amsterdam), L. Izzo (DARK/NBI), J. Bolmer (MPE 
Garching), N. R. Tanvir (Univ Leicester), D. B. Malesani (DTU Space), D. 
Xu (NAO/CAS), D. A. Kann (HETH/IAA-CSIC), J. P. U. Fynbo (DAWN/NBI), 
report on behalf of the Stargate collabaration:

We observed the optical afterglow (Bolmer, GCN 25789) of the INTEGRAL 
GRB 190919B (Mereghetti et al., GCN 25788) using the ESO VLT UT2 
(Kueyen) equipped with the X-shooter spectrograph. Our spectra cover the 
wavelength range 3000-24700 AA, and consist of 4 exposures by 600 s 
each. The observation mid time was 2019 Sep 20.194 UT (4.87 hr after the 
GRB).

In a 30 s image taken with the acquisition camera on Sep 20.1714 UT, we 
detect the optical afterglow, for which we measure a magnitude r = 20.10 
+- 0.02 AB (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 full covered wavelength range. A 
wide trough is visible around 5130 AA, which we identify as due to H I. 
This is confirmed by the presence of the Ly alpha forest blueward of 
this wavelength. We also detect multiple, narrow absorption features 
across all the three arms, which we interpret as due to e.g. S II, Si 
II, O I, S IV, C IV, Fe II, Mg II, Ca I, at a common redshift z = 3.225.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Pedro Figueira, Nestor Jimenez, Camila Navarrete, 
and Juan Carlos Olivares.