[vsnet-grb-info 7665] GRB 090423: VLT/ISAAC spectroscopy

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9219
SUBJECT: GRB 090423: VLT/ISAAC spectroscopy
DATE:    09/04/24 07:20:35 GMT
FROM:    Nial Tanvir at IofA U.Cambridge  <nrt at ast.cam.ac.uk>

N. Tanvir (U. Leicester), A. Levan (U. Warwick), K. Wiersema (U.
Leicester), J. Fynbo, J. Hjorth (DARK/NBI), P. Jakobsson (Reykjavik)
report on behalf of a larger collaboration:

We observed the afterglow of GRB 090423 with ISAAC on the VLT,
beginning about 01:30 (UT), approximately 17.5 hours post-burst.

Our provisional analysis shows a clear continuum at red wavelengths,
but no flux below about 11200A, consistent with a break due to
Lyman-alpha at a redshift z~8.2.  However, we caution that we have not
yet carefully calibrated the instrumental response, and further work
is required to confirm this result.

We thank the VLT observers for their excellent support in obtaining
these data, particularly Valentin Ivanov and Giovanni Carraro.