TITLE: GCN CIRCULAR NUMBER: 10174 SUBJECT: GRB 091117: Magellan optical observations DATE: 09/11/19 06:06:15 GMT FROM: Edo Berger at Harvard E. Berger (Harvard) and J. Mulchaey (OCIW) report: "We obtained optical r-band observations of the BAT error circle of GRB 091117 (GCN #10171) with IMACS on the Magellan/Baade 6.5-m telescope starting on 2009 Nov 19.06 UT. A comparison to DSS images reveals no new sources brighter than the DSS limit of about 21 mag. The galaxy coincident with the XRT source within the BAT error circle (GCN #10173) has a face-on spiral morphology. We find a single apparent point source coincident with one of the spiral arms. This object may be the optical afterglow of GRB091117 or an unrelated bright HII region. Additional observations are planned to determine if the source exhibits fading behavior. An image of the galaxy is available from: http://www.cfa.harvard.edu/~eberger/GRB091117_Magellan.gif