[vsnet-grb-info 5306] GRB 060602A: host redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6997
SUBJECT: GRB 060602A: host redshift
DATE:    07/10/25 12:44:19 GMT
FROM:    Pall Jakobsson at U Hertfordshire  <P.Jakobsson at herts.ac.uk>

Pall Jakobsson (U. Hertfordshire), Daniele Malesani, 
Johan P. U. Fynbo, Jens Hjorth, Paul M. Vreeswijk 
(DARK, NBI) and Nial R. Tanvir (U. Leicester) report 
on behalf of a larger collaboration:

Using FORS1 on the Very Large Telescope, we obtained 
2*20 min spectra (grism 300V+GG375 covering 4000-8000 A) 
of the GRB 060602A host galaxy on 28 December 2006. A firm 
upper limit of z < 2.3 can be placed on the host redshift 
from the lack of Ly-alpha forest lines in the combined 
spectrum.

We do detect a strong emission line at 6664 A. If it 
corresponds to H-alpha at z = 0.015, we would expect to 
detect H-beta and the [O III] doublet in our spectrum. 
However, no features are visible at their predicted 
locations. In addition, this redshift would imply a very 
faint absolute magnitude of M_R = -10.3.

If the emission line corresponds to [O III] 5008 at 
z = 0.331, we would expect to detect [O II] 3728 which we 
do not. The most probable association is with [O II] 3728, 
corresponding to a redshift of z = 0.787. 

Using the relations by Kennicutt (1998, ARA&A, 36, 189), 
the flux of the proposed [O II] line corresponds to a star 
formation rate (SFR) of approximately 1.9 M_Sun/year. This 
value has not been corrected for host extinction, and is 
therefore a strict lower limit to the actual SFR. The 
specific SFR is around 13.6 M_Sun/year (L/L*)^-1, typical 
for GRB host galaxies (Christensen et al., 2004, A&A, 425, 913).