TITLE: GCN CIRCULAR NUMBER: 9078 SUBJECT: GRB 090401B: NOT optical observations DATE: 09/04/01 22:10:33 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani, J.P.U. Fynbo (DARK/NBI), J. Heidt (Heidelberg), T. Liimets (Tartu Observatory), T. Pursimo (NOT), and P. Jakobsson (Univ. Iceland), report on behalf of a larger collaboration: We observed the optical afterglow of GRB 090401B (Schady et al., GCN 9066; Schady & Oates, GCN 9067), also detected by AGILE (Moretti et al., GCN 9069; Giuliani et al., GCN 9075). Observations were carried out in the R band with the Nordic Optical Telescope, starting on April 1.870 UT, 12.3 hr after the GRB. In a single 300 s exposure, the afterglow is clearly detected, with a magnitude R ~ 22.2 +- 0.1, referred to USNO-B1 stars in the neighbourhood. We acknowledge excellent support from the NOT visiting observers and staff.