TITLE:   GCN CIRCULAR
NUMBER:  32778
SUBJECT: GRB 221016A: z-band upper limit, possible afterglow brightening
DATE:    22/10/17 08:56:18 GMT
FROM:    Daniele B Malesani at Radboud U  <d.malesani@astro.ru.nl>

D. B. Malesani (Radboud Univ. and DAWN/NBI), D. A. Kann (Goethe Univ.), 
L. Izzo (DARK/NBI), S. Covino, P. D'Avanzo (INAF/OAB), N. R. Tanvir 
(Univ. Leicester), report on behalf of the Stargate consortium:

We observed the field of GRB 221016A (Page et al., GCN 32774) with the 
ESO VLT UT3 (Melipal), using the acquisition camera of the X-shooter 
spectrograph. A single 30 s image is available to us, taken on 2022 Oct 
17.034 UT (1.17 hr after the trigger). The image seeing was rather poor, 
about 2.2".

No source is detected at the position of the optical counterpart 
discovered by Strausbaugh & Cucchiara (GCN 32775), down to a 3-sigma 
limit z > 20.8 (AB; calibrated against one nearby SkyMapper star). 
Comparison between our limit and the magnitudes reported by Strausbaugh 
& Cucchiara (GCN 32775) seems to indicate a brightening of the afterglow 
between ~1 and ~2 hr after the trigger.

We acknowledge the ESO staff for a quick reaction to our request, in 
particular Matias Jones and Felipe Gaete.