TITLE: GCN CIRCULAR NUMBER: 15187 SUBJECT: GRB 130907A: NOT redshift DATE: 13/09/07 23:44:37 GMT FROM: Antonio de Ugarte Postigo at IAA-CSIC A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), D. Xu (DARK/NBI), D. Malesani (DARK/NBI), J. Gorosabel (IAA-CSIC/UPV-EHU), P. Jakobsson (U. Iceland) and J. Kajava (NOT) report on behalf of a larger collaboration: We observed the optical afterglow of GRB 130907A (Page et al., GCN 15183; Gorbovskoy et al., GCN 15184) with the NOT equipped with the AlFOSC spectrograph and camera. The transient is clearly detected in our acquisition images, taken in a clear filter, at the following coordinates: RA(J2000) = 14:23:34.08 Dec(J2000) = +45:36:26.7 Using R-band values from nearby USNO stars, we get a magnitude R = 16.7 +- 0.1 at a mean time of 0.41 hr after the GRB, where the error is dominated by calibration uncertainties. A single spectrum of 900 s covering the range from 3800 to 8000 AA, with a resolution of ~700, was obtained with a mean epoch of 0.598 hr after the burst. The spectrum presents a strong continuum with deep spectral features of AlIII, FeII, MgII and MgI at a common redshift of z=1.238 (wavelength calibration based on archival data), which we identify as the redshift of the GRB.