[vsnet-grb-info 14006] GRB 130831A: VLT/FORS2 spectroscopic detection of a supernova

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15320
SUBJECT: GRB 130831A: VLT/FORS2 spectroscopic detection of a supernova
DATE:    13/10/09 09:54:39 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose at tls-tautenburg.de>

S. Klose, A. Nicuesa Guelbenzu (both TLS Tautenburg), T. Kruehler (ESO), 
J. Greiner, D. A. Kann, A. Rau (all MPE Garching), F. Olivares E. (UNAB, 
MCSS, Chile), and S. Schulze (PUC, MCSS, Chile), on behalf of a larger 
collaboration report:


We observed the optical transient following GRB 130831A (e.g., Hagen et 
al. 2013, GCN 15139; Guidorzi et al. 2013, GCN 15140; Xu et al. 2013, GCN 
15142; Yoshii et al. 2013, GCN 15143) with VLT/FORS2 equipped with the 
300V grism on Sep 29 and Sep 30, 2013, between 28.5 and 29.5 days after 
the burst under excellent sky conditions with mean seeing around 0.6". The 
total exposure time of the spectrum was 1.53 hr and covers the spectral 
range between approximately 440 and 920 nm.

In the combined spectrum, we detect the optical emission over the full 
spectral range. The spectrum peaks at about 800 nm and shows broad 
absorption features, very much reminiscent of the spectrum of, e.g., GRB 
031203 / SN 2003lw (z=0.1055; Malesani et al. 2004, ApJ 609, L5), and the 
recent GRB 120714B / SN 2012eb (z=0.40; Klose et al. 2012, GCN 13613), GRB 
130215A / SN 2013ez (z=0.597; de Ugarte Postigo et al., GCN 14303), GRB 
130427A / SN 2013cq (z=0.34; Xu et al. 2013, ApJ 776, 98), and GRB 130702 
/ SN 2013dx (z=0.145; Schulze et al. 2013, GCN 14994), all obtained around 
SN maximum light.

We conclude that we have spectroscopically discovered the appearence of a 
broad-line SN following GRB 130831A at z=0.4791 (Cucchiara et al. 2013, 
GCN 15144), confirming the conclusion of Pozanenko et al. (GCN 15237) 
based on the optical light curve.