GCN Circular 22029
D. Malesani (DARK/NBI), M. Stone (Turku Univ.), K. Karhunen (Turku Univ.), A. de Ugarte Postigo (IAA/CSIC and DARK/NBI), and D. Xu (NAOC/CAS), report on behalf of a larger collaboration: We observed the field of GRB 171020A (Page et al., GCN 22028) with the Nordic Optical Telescope equipped with the AlFOSC imager and spectrograph. Observations were carried out in the r and z filters, starting on 2017 Oct 20.979 UT (22.9 min after the trigger). Within the XRT error circle, we detect an uncatalogued source at coordinates (J2000): RA = 02:36:59.62 Dec = +15:12:16.0 By comparison with nearby stars from the Pan-STARRS catalog, we measure r = 20.98 +- 0.03 AB. As this object is not visible in the deeper, archival Pan-STARRS images, and given the coincidence with the X-ray counterpart, we suggest this object to be the optical afterglow of GRB 171020A.