GCN Circular 33110
Subject
GRB 221226B: VLT/X-shooter redshift and host galaxy
Date
2022-12-27T09:26:14Z (a year ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
D. Xu (NAOC), A. Chrimes (Radboud Univ.), B. Schneider (MIT), L. Izzo
(DARK/NBI), A. Saccardi (GEPI, Observatoire de Paris), Z.P. Zhu (NAOC,
HUST), N.R. Tanvir (Univ. Leicester) report on behalf of the Stargate
collaboration:
We observed the field of GRB 221226B detected by Swift (Cenko et al.,
GCN 33108) and Fermi (Fermi GBM team, GCN 33107) 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.
The observations started at 01:10:06 UT on 2022-12-27, i.e., ~2.48 hr
after BAT trigger. The optical afterglow of the burst is detected at
coordinates
R.A.(J2000) = 01:31:38.036
Dec.(J2000) = - 41:31:37.25
with an uncertainty of ~0.3 arcsec and r = 22.0 +/- 0.1 mag, calibrated
with Legacy Survey nearby stars.
A broad absorption feature is visible around 4490 AA, which we identify
as being due to H I. From detection of multiple absorption features,
which we interpret as being due to S II, Si II, O I, C II, Si IV, Al
III, NV, and emission features due to [O II] and Hbeta, we infer a
common redshift of z = 2.694. We conclude this is the redshift of the burst.
Note that at the optical afterglow position, the Legacy Survey presents
an extended source with r = 23.82 mag, which is likely the host galaxy
of the burst, being consistent with the the detection of emission
features in the X-shooter spectra.
We acknowledge excellent support from the ESO observing staff in
Paranal, in particular Pascale Hibon and Ditte Slumstrup.