[IAUC] CBET 3529: 20130516 : SUPERNOVA 2013cq = GRB 130427A

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                                                  Electronic Telegram No. 3529
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
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SUPERNOVA 2013cq = GRB 130427A
     A. de Ugarte Postigo, Instituto de Astrofisica de Andalucia (IAA),
Consejo Superior de Investigaciones Cientificas (CSIC) and Dark Cosmology
Centre, Niels Bohr Institute, University of Copenhagen; D. Xu, Dark Cosmology
Centre; G. Leloudas, Oskar Klein Centre (OKC), Stockholm University, and Dark
Cosmology Centre; T. Kruehler and D. Malesani, Dark Cosmology Centre; J.
Gorosabel, IAA/CSIC and Universidad del Pais Vasco University of the Basque
Country; C. C. Thoene and R. Sanchez-Ramirez, IAA/CSIC; S. Schulze, Pontificia
Universidad Catolica de Chile and Millennium Center for Supernova Science;
J. P. U. Fynbo and J. Hjorth, Dark Cosmology Centre; Z. Cano and P. Jakobsson,
University of Iceland; and A. Cabrera-Lavers, Instituto de Astrofisica de
Canarias, Universidad de La Laguna, on behalf of a larger collaboration,
report that they have been monitoring the optical counterpart of GRB 130427A
(discovered with the Swift spacecraft; cf. Maselli et al., GCN Circular 14448,
posted at website URL http://gcn.gsfc.nasa.gov/gcn3/14448.gcn3; and Elenin et
al., GCN 14450).  The authors obtained spectroscopy of the optical counterpart
and the burst's host galaxy with the 10.4-m Gran Telescopio Canarias (GTC) at
Roque de los Muchachos Observatory in La Palma, Spain, 16.7 days after the
onset of the gamma-ray outburst; this is 12.5 days in the host-galaxy rest
frame (z = 0.34; cf. Levan et al., GCN 14455; Xu et al., GCN 14478; Flores et
al., GCN 1449).
     Observations consisted of four 1200-s exposures with the R500R grism,
covering the range 480-1000 nm with a resolution of about 600.  The slit was
oriented to cover both the afterglow and the host-galaxy center.  The spectrum
has a strong contribution from the host galaxy.  To overcome this, they built
a synthetic host-galaxy spectrum based on the Sloan Digital Sky Survey (DR9)
photometry using LePhare (version 2.2; Arnouts et al. 1999, MNRAS 310, 540;
Ilbert et al. 2006, A.Ap. 457, 841).  They then subtracted this host-galaxy
template from the GTC spectrum to obtain a "clean" spectrum of the
counterpart associated with GRB 130427A.  The resulting spectrum is that of a
broad-lined type-Ic supernova, with a prominent bump at about 680.0 nm in the
observer frame.  In particular, they obtained an excellent match with the
spectrum of SN 2010bh at 12.7 (rest-frame) days after GRB 100316D (Bufano et
al. 2012, Ap.J. 753, 67).
     The authors stress that this conclusion is independent of the host-galaxy
model adopted.  By running SNID (Blondin and Tonry 2007, Ap.J. 666, 1024) on
the original spectrum (i.e., including host contamination), they still obtain
good matches with a series of broad-lined type-Ic supernovae, including with
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 around 34000 km/s at similar
phases (Bufano et al. 2012, Ap.J. 753, 67), which the present suggest is also
the case for the supernova associated with GRB 130427A, here designated SN
2013cq.  A figure of their preliminary analysis can be seen at website URL
http://www.iaa.es/~deugarte/GRBs/130427A/130427A_GTC.jpg.  The authors
acknowledge excellent support from the GTC staff.


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                         (C) Copyright 2013 CBAT
2013 May 16                      (CBET 3529)              Daniel W. E. Green