Electronic Telegram No. 3531
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
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SUPERNOVA 2013cq = GRB 130427A
     [Editor's note:  the following text replaces that on CBET 3529
(optical positional information added from the date of outburst).]
     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, who noted mag about 12 on presumably unfiltered optical CCD
images taken on Apr. 27.327 UT, providing the position of the optical
afterglow as R.A. = 11h32m32s.84, Decl. = +27d41'56".2, equinox 2000.0).  The
authors of this item 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.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2013 CBAT
2013 May 18                      (CBET 3531)              Daniel W. E. Green