TITLE: GCN CIRCULAR NUMBER: 20988 SUBJECT: GRB 170405A: NOT optical observations DATE: 17/04/06 01:22:36 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst Daniele Malesani (DARK/NBI), K. E. Heintz (DARK/NBI and Univ. Iceland), and Tapio Pursimo (NOT) report on behalf of a larger collaboration: We observed the optical afterglow of GRB 170405A (Troja et al., GCN 20984; Hui & Meegan, GCN 20986; Vianello & Kocevski, GCN 20987) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Observations were carried out in the SDSS griz filters, with a sub-optimal PSF (1.6-2.0"). Inspection of the r-band image (with mean time Apr 6.01 UT, that is 5.47 hr after the trigger) clearly shows the optical afterglow first localized by UVOT (Troja et al., GCN 20984), which has now faded to r = 21.05 +- 0.08 AB, calibrated against nearby stars from the Pan-STARRS catalog. In our images, the afterglow coordinates are perfectly consistent with the UVOT values: RA(J2000) = 14:39:18.72 Dec(J2000) = -25:14:35.3 We also note the presence of a nearby object approximately 2.3" W of the afterglow, also visible in the Pan-STARRS archival images (with a Pan-STARRS magnitude r = 21.82 +- 0.19 AB). Its relation to the GRB is not clear, but its proximity may affect the afterglow photometry.