GCN Circular 31075
Subject
Short GRB 211106A: spectroscopy of galaxies in the field
Event
Date
2021-11-11T10:49:00Z (4 years ago)
From
Daniele B Malesani at Radboud U <d.malesani@astro.ru.nl>
L. Christensen (DAWN/NBI), L. Izzo (DARK/NBI), P. Schady (Univ. Bath),
D. B. Malesani (Univ. Radboud and DAWN/NBI), P. D'Avanzo (INAF/OABr), A.
J. Levan (Radboud Univ.), S. Campana (INAF/OABr), D. Alexander Kann
(HETH, IAA/CSIC), report on behalf of the Stargate consortium:
We observed the field surrounding the candidate afterglow (source #2) of
the short GRB 211106A (Tohuvavohu et al., GCN 31049; D'Elia et al., GCNs
31051, 31068) with the ESO VLT equipped with the MUSE panoramic
integral-field spectrograph, covering a square 1'x1' region around the
XRT position. Spectra of each spaxel cover the wavelength range
4750-9350 AA. The mean time of our observation was November 10.03 UT
(3.84 days after the GRB).
We report the redshift of three galaxies close to the XRT error circle
(D'Elia et al., GCN 31068; see also Malesani et al., GCN 31070):
#1)
RA = 22:54:20.29
Dec = -53:13:53.6
z = 0.097 as inferred by the detection of the [O iii] doublet and Hbeta
in emission.
The projected separation from the center of the XRT error circle is
4.8", or 8.6 kpc at z = 0.097.
A bright, pointlike object (RA = 22:54:20.32, Dec = -53:13:56.7) is
spatially blended with this galaxy, which we confirm to be a star thanks
to the detection of Balmer and Ca II absorption at z = 0.
#2)
RA = 22:54:21.31
Dec = -53:13:47.2
z = 0.294 as inferred by the detection of the [O iii] doublet and Hbeta
in emission.
The projected separation from the center of the XRT error circle is
7.9", or 34.9 kpc at z = 0.294.
#3)
RA = 22:54:20.34
Dec = -53:13:40.8
z = 1.012 as inferred by the detection of the (resolved) [O ii] doublet
in emission.
The projected separation from the center of the XRT error circle is
8.3", or 67.0 kpc at z = 1.012.
While the association of these sources with GRB 211106A cannot be
confirmed based on our data, object #1 has the smallest chance
association probability. With R ~ 21.5, using the formula by Bloom et
al. (2002, AJ, 123, 1111), we compute a chance association probability
of ~5%.
Stacking the MUSE cube along the wavelength axis, faint emission is also
detected inside the XRT error circle, consistent with our FORS2 image
(Malesani et al., GCN 31070). The S/N is too low to extract any spectral
information, and no emission lines are identified.
An image showing the position of the three galaxies can be viewed at the
following link:
https://www.astro.ru.nl/~dmalesani/GRB/211106A/GRB211106A_galaxies.jpg
We acknowledge expert support from the observing staff at Paranal, in
particular Thomas "Rivi" Rivinius, Thomas Wevers, Israel Blanchard, Juan
Carlos Olivares, and Joe Anderson.