[vsnet-grb-info 6745] GRB 081008: VLT/FORS2 spectroscopy

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8345
SUBJECT: GRB 081008: VLT/FORS2 spectroscopy
DATE:    08/10/09 03:32:02 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

P. D'Avanzo (INAF-OAB), V. D'Elia (INAF-OAR), S. Covino (INAF-OAB) 
report, on behalf of the MISTICI collaboration:

Following the detection of GRB 081008 (Rykoff, GCN 8343; Racusin et al., 
GCN 8344), we triggered observations with the FORS2 camera, mounted at 
ESO-VLT. The observations were performed using the 600B grism. We took a 
900 s spectrum starting around Oct 09 at 00:20 UT (about 4.5 hours after 
the burst) and covering the range 380-620 nm.

The non-detection of Ly-alpha sets an upper limit of z ~ 2 to the GRB 
redshift. We detect a double horned absorption feature around lambda 
4600 A which we identify as the MgII doublet at 2796-2803 A. This 
implies a redshift of the absorber of z = 0.64. We also detect two 
absorption features around lambda 4530-4550 A which we identify as FeII 
2586 and FeII 2600 A. We possibly interpret this signature as another 
absorption system at z = 0.75.

However, at the present stage, the most robust redshift range that we 
can set for GRB 081008 is 0.64 < z < 2.

Further analysis is in progress.

We are very grateful for the excellent support of the VLT staff.