TITLE:   GCN CIRCULAR
NUMBER:  22166
SUBJECT: GRB 171123A: OSN Upper Limit
DATE:    17/11/24 18:52:37 GMT
FROM:    Luca Izzo at IAA-CSIC  <Luca.Izzo@ICRA.it>

L. Izzo, D. A. Kann, A. de Ugarte Postigo (all HETH/IAA-CSIC), and V. Casanova (IAA-CSIC)  report:

We observed the field of GRB 171123A  (Evans et al.; GCN Circ. 22148) with the 1.5-m OSN telescope in Granada, Spain.

We began observing at 03:32:53 UT (13.3 hours after the GRB trigger), and obtained 18x300s images in the Ic band. Observations were obtained in inclement conditions (clouds, bad seeing of ~2")  and the last four images could not be used.

In our stacked image, we find no source at the position reported by Schmidl et al. (GCN Circ. 22162) down to a a 3-sigma limit of Ic (Vega) > 21.  The calibration was performed using nearby stars in the USNO B1 catalog.