D. Malesani (DARK/NBI), H. Flores (GEPI/Paris obs.), A. J. Levan (Univ.
Warwick), D. Xu (NAOC/CAS), N. R. Tanvir (Univ. Leicester), and J. P. U.
Fynbo (DARK/NBI), report:
We observed the field of GRB 170311A (Cummings et al., GCN 20846) with
the VLT/UT2 (Kueyen), using the acquisition camera of the X-shooter
spectrograph. Observations started approximately on March 11.366 UT,
that is around 38 min after the GRB trigger. Imaging was carried out
using the SDSS z filter.
No source is detected within or close to the UVOT-enhanced XRT position
(Osborne et al., GCN 20850), down to a 3-sigma limiting magnitude z = 21
AB, calibrated against nearby stars from the Pan-STARRS catalog
(Chambers et al. 2016, arXiv: 1612.05560). Our result is consistent with
other reports (e.g., Wiseman & Schady, GCN 20853).
We acknowledge excellent support from the ESO observing staff at
Paranal, in particular Marcelo Lopez, Joe Anderson, and George Hau. We
also acknowledge the team of the Gaia-ESO survey (ESO program
197.B-1074, PI Gilmore), for generously and consistently accepting to
carry out ToO observations during their allocated nights.