TITLE: GCN CIRCULAR NUMBER: 28376 SUBJECT: GRB 200906A: OSN 1.5m Upper Limit DATE: 20/09/07 03:31:53 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), and V. Casanova (IAA-CSIC) report: We observed the location (Beardmore et al., GCN #28373) of the Swift GRB 200906A (Page et al., GCN #28371; GBM detection: Fermi GBM Team, GCN #28370, Hamburg et al., GCN #28374) with the 1.5m telescope of the Observatorio Sierra Nevada, in Granada, Spain. We obtained 78 x 100 s images beginning 2020-09-06 21:29:03.51 UT, after clouds had cleared. In a stack of all images, centered at 0.39467 days after the GRB, no source is detected at the enhanced XRT position. Measured against two nearby USNO-B1.0 stars, we derive an upper limit of Ic > 23.4 mag. This agrees with the non-detection reported by Fu et al. (GCN #28372). We note the refined XRT analysis (Beardmore et al., GCN #28375) also reports an NH column density significantly exceeding the Galactic value, indicating this is a dark GRB.