GCN Circular 11307
A. de Ugarte Postigo (DARK/NBI), H. Flores (Paris Obs.), K. Wiersema (U. Leicester), C.C. Thoene (NBIA), J.P.U. Fynbo (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA) report on behalf of the X-shooter GRB collaboration: We have observed the optical source related to GRB 100925A/MAXI J1659-152 (Mangano et al. GCN Circ. 11296, Marshall et al. GCN Circ. 11298) using the X-shooter spectrograph mounted at the Kueyen telescope of ESO's VLT (Paranal Observatory, Chile). The spectrum consists of a combined exposure of 2x600s and was started at 23:40 UT on September 25. The spectrum covers the complete range from 3000 to 24800 angstroms. In a preliminary analysis we identify broad emission lines from the Balmer series of hydrogen and HeII as well as CaII and Na I absorption from the ISM of the MW, all at redshift zero. The emission lines have a width of about 2000 km/s showing a double peak profile. The spectrum is consistent with that of an X-ray binary and we hence confirm that GRB 100925A/MAXI J1659-152 is a Galactic source (Kann GCN Circ. 11299, Negoro et al. ATEL 2873). We thank the Paranal staff for excellent support, in particular Claudio Melo.