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GCN Circular 9958

GRB 090927: VLT redshift
2009-09-28T07:44:23Z (15 years ago)
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <>
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 
GRB 090927.

We acknowledge excellent support from the ESO observing staff, in 
particular Yuri Beletsky and Stephane Brillant.
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