SN 2013dx associated with GRB 130702A: a detailed photometric and spectroscopic monitoring and a study of the environment^⋆,⋆⋆

¹ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
e-mail: delia@mporzio.astro.it
² ASI-Science Data Center, via del Politecnico snc, 00133 Rome, Italy
³ INAF–Istituto di Astrofisica Spaziale e Fisica Cosmica, via P. Gobetti 101, 40129 Bologna, Italy
⁴ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
⁵ INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁶ INAF–Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁷ ICRANET, Piazza della Republica 10, 65122 Pescara, Italy
⁸ ARI, Liverpool John Moores University, IC2 Liverpool Science Park 146 Brownlow Hill, Liverpool, L3 5RF, UK
⁹ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁰ Max-Planck Institute for Astrophysics, Garching, Karl-Schwarzschild-Str. 1, Postfach 1317, 85741 Garching, Germany
¹¹ Millennium Institute of Astrophysics, Casilla 36-D, Santiago, Chile
¹² Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile
¹³ Dark Cosmology Center, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
¹⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

Received: 20 November 2014
Accepted: 17 February 2015

Abstract

Aims. Long-duration gamma-ray bursts (GRBs) and broad-line, type Ic supernovae (SNe) are strongly connected. We aim at characterizing SN 2013dx, which is associated with GRB 130702A, through a sensitive and extensive ground-based observational campaign in the optical-IR band.

Methods. We monitored the field of the Swift GRB 130702A (redshift z = 0.145) using the 8.2 m VLT, the 3.6 m TNG and the 0.6 m REM telescopes during the time interval between 4 and 40 days after the burst. Photometric and spectroscopic observations revealed the associated type Ic SN 2013dx. Our multiband photometry allowed constructing a bolometric light curve.

Results. The bolometric light curve of SN 2013dx resembles that of 2003dh (associated with GRB 030329), but is ~10% faster and ~25% dimmer. From this we infer a synthesized ⁵⁶Ni mass of ~0.2 M_⊙. The multi-epoch optical spectroscopy shows that the SN 2013dx behavior is best matched by SN 1998bw, among the other well-known low-redshift SNe associated with GRBs and XRFs, and by SN 2010ah, an energetic type Ic SN not associated with any GRB. The photospheric velocity of the ejected material declines from ~2.7 × 10⁴ km s^-1 at 8 rest frame days from the explosion, to ~3.5 × 10³ km s^-1 at 40 days. These values are extremely close to those of SN1998bw and 2010ah. We deduce for SN 2013dx a kinetic energy of ~35 × 10⁵¹ erg and an ejected mass of ~7 M_⊙. This suggests that the progenitor of SN2013dx had a mass of ~25–30 M_⊙, which is 15–20% less massive than that of SN 1998bw. Finally, we studied the SN 2013dx environment through spectroscopy of the closeby galaxies: 9 out of the 14 inspected galaxies lie within 0.03 in redshift from z = 0.145, indicating that the host of GRB 130702A/SN 2013dx belongs to a group of galaxies, an unprecedented finding for a GRB-associated SN and, to our knowledge, for long GRBs in general.