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GCN Circular 14646

Subject
GRB 130427A: Spectroscopic detection of the SN from the 10.4m GTC
Date
2013-05-14T21:21:33Z (11 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), D. Xu (DARK/NBI), 
G. Leloudas (OKC, Stockholm, DARK/NBI),  T. Kruehler, 
D. Malesani (DARK/NBI), J. Gorosabel (IAA-CSIC, UPV/EHU), Z. Cano (U. Iceland),
C.C. Thoene, R. Sanchez-Ramirez (IAA-CSIC), S. Schulze (PUC and MCSS), 
J.P.U. Fynbo, J. Hjorth (DARK/NBI), P. Jakobsson (U. Iceland) and 
A. Cabrera-Lavers (IAC-ULL) report on behalf of a larger collaboration:

We obtained spectroscopy of the optical counterpart and host galaxy of 
GRB 130427A (Maselli et al., GCN 14448; Elenin et al., GCN 14450) with the 
10.4m GTC telescope, 16.7 days after the GRB onset. This is 12.5 days in the 
host galaxy rest-frame (z = 0.34; Levan et al. GCN 14455, Xu et al. GCN 14478 
and Flores et al. GCN 1449). Observations consisted of 4x1200s with the 
R500R grism, covering the range between 4800 and 10000 AA with a 
resolution of ~600. The slit was oriented to cover both the afterglow and the 
host galaxy centre.

The spectrum has a strong contribution from the host galaxy. To overcome this, 
we built a synthetic host galaxy spectrum based on the SDSS (DR9) photometry 
using LePhare (version 2.2, Arnouts et al. 1999, MNRAS, 310, 540; Ilbert et al. 
2006, A&A, 457, 841). We then subtracted this host galaxy template from the 
GTC spectrum to obtain a "clean" spectrum of the counterpart associated to GRB 
130427A.

The resulting spectrum is that of a broad-lined Ic SN, with a prominent bump at 
~6800 A observer frame. In particular, we obtain an excellent match with the 
spectrum of  SN 2010bh at 12.7 (rest-frame) days after GRB 100316D 
(Bufano et al. 2012, ApJ 753, 67).

We stress that this conclusion is independent of the host galaxy model 
adopted. By running SNID (Blondin & Tonry 2007, ApJ, 666, 1024) on the 
original spectrum (i.e. including host contamination), we still obtain good 
matches with a series of broad-lined Type Ic SNe, including SNe 1998bw, 
1997ef, 2002ap and 2006aj, albeit at a lower redshift. The fact that SNID 
suggests a lower redshift  is explained by the fact that SN 2010bh had high 
expansion velocities, reaching ~34000 km/s at similar phases (Bufano et al. 
2012, ApJ 753, 67), which we suggest is also the case for the SN associated 
with GRB 130427A.

A figure of our preliminary analysis can be seen at:

http://www.iaa.es/~deugarte/GRBs/130427A/130427A_GTC.jpg

We acknowledge excellent support from the GTC staff.

[GCN OPS NOTE(14may13): Per author's request, ZCwas added to the author list.]
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