TITLE:   GCN CIRCULAR
NUMBER:  7997
SUBJECT: TNG/DOLORES redshift for GRB080721
DATE:    08/07/21 23:16:34 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>

P. D'Avanzo (INAF-OAB), V. D'Elia (INAF-OAR), G. Adreuzzi, G. Tessicini 
(INAF-TNG), L. A. Antonelli, F. Fiore (INAF-OAR), D. Fugazza, C. 
Guidorzi (INAF-OAB) and G. Chincarini (Univ. Bicocca) report, on behalf 
of the CIBO collaboration:

Following the Swift detection of GRB080721 (Marshall et al., GCN 7988), 
we triggered observations with the DOLORES low resolution spectrograph, 
mounted at the Italian TNG telescope located in the Canary Islands 
(Spain). The observations were performed using the LR-B grism. We took a 
1800 s spectrum starting around Jul 21 at 21:30 UT (about 11.0 hours 
after the burst) and covering the range 300-780 nm with a resolution of 
R ~ 600.

A preliminary analysis of the spectra shows a broad absorption feature 
at lambda_obs ~ 440 nm (based on a preliminary wavelength calibration). 
Interpreting this feature as Ly-alpha we infer a redshift z = 2.602, in 
agreement with the UVOT photometric redshift estimate (Holland et al., 
GCN 7991; Ward et al. GCN 7996). At this redshift we can detect also 
(rest frame) other absorption features like: CII (133.4 nm), SiIV 
doublet (139.3-140.2 nm), SiII (152.6 nm), CIV doublet (154.8-155.0 nm).

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