GCN Circular 31070
Subject
GRB 211106A: VLT/FORS2 optical observations
Date
2021-11-09T23:17:48Z (3 years ago)
From
Daniele B Malesani at Radboud U <d.malesani@astro.ru.nl>
Daniele B. Malesani (Radboud Univ. and DAWN/NBI), Paolo D'Avanzo
(INAF/OABr), Andrew J. Levan (Radboud Univ.), Ana Nicuesa Guelbenzu (TLS
Tautenburg), report on behalf of the Stargate consortium:
We observed the location of XRT source #2 (D'Elia et al., GCNs 31051,
31068), indicated as the X-ray afterglow of the short GRB 211106A
(Tohuvavohu et al., GCN 31049; Ridnaia et al., GCN 31054; Fletcher, GCN
31055) using the ESO VLT UT1 equipped with the FORS2 camera. A total of
20 minutes on source were obtained in the R band, with mid time 2021 Nov
9.116 UT (that is, 2.92 days after the GRB).
No bright sources are detected inside the XRT error circle, down to R >
26.2 (Vega, preliminary calibration based on faint USNO-B1 stars).
However, there are two extended (FWHM ~ 2") objects at the following
coordinates:
RA = 22:54:21.31
Dec = -53:13:47.2
RA = 22:54:20.29
Dec = -53:13:53.6
The second one is partially blended with a brighter star. These two
galaxies are 7.9" and 4.8" away, respectively, from the center of the
XRT position (which has currently a 90% uncertainty radius of 3.4"). A
faint extension of the most nearby object, or a separate, very faint
source, is also marginally detected inside the XRT error circle.
Should the GRB be associated with one of the closeby galaxies, this
would indicate a relatively low redshift. Lacking a reference image, we
cannot yet ascertain whether a faint transient could be present,
superposed on top of the galaxy light. Chandra X-ray observations would
help pinpoint the precise location of the source.
We acknowledge excellent support from the ESO staff at Paranal, still
operating at reduced capacity because of the COVID pandemic, in
particular Eleonora Sani, Aleksandra Solarz, Rodrigo Palominos, Pedro
Figuera and Thomas Rivinius.