TITLE:   GCN CIRCULAR
NUMBER:  17697
SUBJECT: GRB 150413A: redshift determination with the 2.2m CAHA
DATE:    15/04/14 10:34:25 GMT
FROM:    Alberto Castro-Tirado at Inst.de Astro. de Andalucia  <ajct@iaa.es>

R. Sanchez-Ramirez (UPV/EHU, IAA-CSIC), A. J. Castro-Tirado (IAA-CSIC,
ISA-UMA), F. Hoyos and J. Aceituno (CAHA), on behalf of a larger
collaboration, report:

Following the detection of GRB 150413A by Swift (Markwardt et al. GCNC
17688) we have obtained a 1200s+1800s spectrum at the position of the
optical afterglow (Ivanov et al. GCNC 17689, Serino et al. GCNC 17691,
Schmalz et al. GCNC 17692, Xu et al. GCNC 17693, Klose et al. GCNC 17694).
Observations were carried out with the 2.2m CAHA telescope (+ CAFOS) at
the German-Spanish Calar Alto Observatory, starting at 20:25 UT. (i.e. 6.5
hr post-burst) under poor weather and seeing conditions. After a
preliminary reduction, we have detected a broad absorption line which we
identify as Lyman-alpha at a reshift of z = 3.2. Due the low SNR of the
combined spectrum, we only detect several lines at low significance (Ni
II, Si IV, C IV, Fe II,…) consistent with this redshift, which we propose
to be the redshift of GRB 150413A.

We acknowledge excellent support of the CAHA staff.