TITLE: GCN CIRCULAR NUMBER: 21346 SUBJECT: GRB 170714A: z-band afterglow candidate for OSIRIS/GTC DATE: 17/07/15 06:37:17 GMT FROM: Antonio de Ugarte Postigo at IAA-CSIC A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann L. Izzo, C. C. Thoene (HETH/IAA-CSIC), N. Castro-Rodriguez (GTC, IAC, ULL), A. Marante, J. A. Melian (GTC) report: We observed the field of GRB 170714A (D'Ai et al. GCN 21340), an ULGRB or RTDE candidate (Kann et al., GCN 21345) with OSIRIS at the 10.4m GTC telescope in La Palma (Spain). Observations consisted in several short exposures in i and z filters. The observations were not easy, as the field was located 30 deg away from the 68% illuminated Moon, implying a very high background. In the combined z-band frame, with mean epoch at 05:10:24 UT (16.75 hr after the burst) we detect a single object within the refined XRT error box (Evans et al. GCN 21341) which is not present in PanSTARRS imaging, with coordinates (J2000): R.A.: 02:17:23.99 Dec.: +01:59:29.51 and a magnitude of z(AB)=22.3+/-0.2, which we identify as the possible GRB afterglow, although we cannot make any statement about variability at this time. In our preliminary analysis we do not detect the object in any other band, implying a possible strong reddening. Further follow up, especially in NIR bands is encouraged.