Andrew J. Levan (Univ. Warwick), Johan P.U. Fynbo (DARK/NBI), Jens
Hjorth (DARK/NBI), Daniele Malesani (DARK/NBI), Paolo D'Avanzo
(INAF/OABr), Valerio D'Elia (INAF/OAR), report on behalf of a larger
We observed the afterglow of GRB 090927 (Grupe et al., GCN 9945;
Gronwall et al., GCN 9946), possibly short (Stamatikos et al., GCN
9955). Using FORS2 on the Very Large Telescope, we have obtained 3x30
min spectra (300V grism) of the optical afterglow (Gronwall & Grupe, GCN
9946; Klotz et al., GCN 9956). Observations started on Sep 27.11 UT,
about 16.5 hr after the burst. The afterglow had a magnitude R ~ 21.7 as
measured from the acquisition images.
The obtained spectrum shows Mg II and Fe II absorption lines
corresponding to z = 1.37. There is no evidence for higher redshift
systems or a Lyman-alpha and hence z = 1.37 is the likely redshift of
We acknowledge excellent support from the ESO observing staff, in
particular Yuri Beletsky and Stephane Brillant.