TITLE:   GCN CIRCULAR
NUMBER:  31063
SUBJECT: MeerLICHT follow-up of GRB 211106A
DATE:    21/11/09 10:31:00 GMT
FROM:    Simon de Wet at UCT  <dwtsim002@myuct.ac.za>

S. de Wet (UCT), P.M. Vreeswijk (Radboud), A.J. Levan (Radboud),

P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT

consortium and the Stargate collaboration:


We observed the field of the Swift/BAT-GUANO short GRB candidate

GRB211106A (Tohuvavohu et al., GCN 31049) with the 0.6m wide-field

MeerLICHT optical telescope located at Sutherland, South Africa,

taking 10x60s exposures in the q-band starting at 2021-11-06,

18:37:17 UT, approximately 14 hours after the GRB trigger.


We co-added the images to reach a full-frame 5-sigma AB limiting

magnitude of q = 21.90. An archival reference image with limiting

magnitude of q = 20.54 was used to perform image subtraction

through our transient detection pipeline. The MeerLICHT field-of-view

fully covers the BAT-GUANO error box and includes all the X-ray

sources found through Swift-XRT follow-up observations

(D'Elia et al., GCN 31051).


Our transient pipeline finds 1 candidate in the BAT-GUANO error

box, at the same position as the XRT source coincident with a known

X-ray source. The coordinates of the transient coincide with a star

with brightness G = 17.49 in the Gaia EDR3 catalogue, spatially

very close to galaxy LEDA 432583. We believe the transient detection

is due to the star showing variable behaviour rather than a transient

in the galaxy, owing to an increase in brightness of the star from

q = 17.73 mag in the reference image to q = 17.47 in the new image.

We detect no source in our images at the position of the known X-ray

source 1RXS J225507.9-531312.


No other promising transient candidates are found in the error boxes

of the 9 XRT sources nor the BAT-GUANO error box, down to a transient

limiting magnitude of 20.34.


There is one other potential transient candidate in our FOV, but it

is 15.6��� away from the centre of the BAT-GUANO error box, so unlikely

to be associated with GRB 211106A. The coordinates are

RA, Dec (J2000) = 22:54:17.88, -52:58:35.22. The Legacy Survey DR9

images show a spiral galaxy at this position, which could be showing

variable behaviour or may be due to a transient near the galaxies' core.


MeerLICHT is built and run by a consortium consisting of Radboud

University, University of Cape Town, the South African Astronomical

Observatory, the University of Oxford, the University of Manchester

and the University of Amsterdam.