TITLE: GCN CIRCULAR NUMBER: 6398 SUBJECT: GRB 070508: OA fading and tentative redshift DATE: 07/05/09 15:11:02 GMT FROM: Pall Jakobsson at U Hertfordshire Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo (DARK, NBI), Michael I. Andersen (Potsdam), Andreas O. Jaunsen (U. Oslo), Christina C. Thoene, Darach Watson, Jens Hjorth, Bo Milvang-Jensen (DARK, NBI), Nial R. Tanvir (U. Leicester) and P. Moller (ESO) report on behalf of a larger collaboration: Using FORS1 on the Very Large Telescope, we have obtained 3*30 min spectra (grism 300V) of GRB 070508 (Grupe et al., GCN 6383). The UVOT optical afterglow candidate (Marshall & Grupe, GCN 6392) has clearly faded in our acquisition image. Using photometric zeropoints from the ESO webpages we estimate the afterglow magnitude to be R ~ 22.0 on May 8.337 (3.79 hours post-burst). The combined spectrum does not display any obvious absorption features. However, a firm upper limit of z < 2.3 can be placed on the redshift of GRB 070508 from the lack of Ly-alpha forest lines in the spectrum of the afterglow. This is consistent with the UVOT observations (Marshall & Grupe, GCN 6392). We do detect a tentative emission line at 6781 A. If it corresponds to H-alpha at z = 0.033, we would expect to detect H-beta and the [O III] doublet in our spectrum. However, no features are visible at their predicted locations. The most probable association is with [O II] 3728, corresponding to a redshift of z = 0.82. We caution that the magnitude reported above is then most likely affected by host galaxy emission. We thank the Paranal staff for excellent support.