GCN Circular 31075

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
Not found
 
 
; D'Elia et al., GCNs 
31051
Not found
 
 
, 31068
Not found
 
 
) 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
Not found
 
 
; see also Malesani et al., GCN 31070
Not found
 
 
):

#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
Not found
 
 
). 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.