TITLE: GCN CIRCULAR NUMBER: 22660 SUBJECT: GRB 180418A: NOT optical observations DATE: 18/04/19 00:20:53 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst Daniele Malesani (DAWN/NBI and DARK/NBI), Kasper Elm Heintz (Univ. Iceland and DAWN/NBI), Maria Stone (Univ. Turku), and James Stone, report on behalf of a larger collaboration: We observed the optical afterglow (Zheng & Filippenko, GCN 22647; Guidorzi et al., GCN 22648; Troja et al., GCN 22652; Fong et al., GCN 22659) of GRB 180418A (D'Elia et al., GCN 22646) with the 2.5-m Nordic Optical Telescope (NOT) equipped with StanCam. Observations were carried out in the Bessel R filter, but calibrated against SDSS r-band Pan-STARRS local photometry. A low S/N source is detected at a position consistent with previous reports. At a mid time of April 18.936 UT (15.72 hr after the trigger), we measure for the counterpart r = 22.70 +- 0.15 AB. Compared to the Gemini-North measurement (Fong et al., GCN 22659), we infer a decay slope alpha = 0.75 +- 0.17, assuming F(t) propto t^-alpha.