TITLE: GCN CIRCULAR NUMBER: 23195 SUBJECT: GRB 180904A: NOT optical observations, candidate host galaxy DATE: 18/09/04 23:04:27 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), Sune Dyrbye (NOT), report on behalf of a largert collaboration: We observed the field of GRB 180904A (D'Ai' et al., GCN 23194) with the Nordic Optical Telescope (NOT) equipped with the AlFOSC camera. In an image of 300 s exposure taken with the SDSS r filter and commencing on Sep 4.9057 UT (15.6 min after the GRB), we detect a single object consistent with the currently available XRT position (http://www.swift.ac.uk/xrt_positions/). Its coordinates are (J2000): RA = 18:16:59.74 Dec = +46:37:47.1 Compared to nearby stars from the Pan-STARRS survey, we measure for this object a magnitude r = 22.56 +- 0.08 AB. We note that the same object is visible in the archival Pan-STARRS image of this field, with a measured magnitude r = 22.84 +- 0.15 AB. There is thus only marginal indication of excess flux in the NOT image. If this object is related to GRB 180904A, as suggested by the spatial coincidence with the X-ray position, it is largely or entirely dominated by the host galaxy. Further observations are planned.