The optical SN 2012bz associated with the long GRB 120422A^⋆

¹ INAF – Brera Astronomical Observatory, via E. Bianchi 46, 23807 Merate (LC), Italy
e-mail: andrea.melandri@brera.inaf.it
² Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
³ INAF – Trieste Astronomical Observatory, via G.B. Tiepolo 11, 34143 Trieste, Italy
⁴ INFN, Sezione di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
⁵ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofisica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁷ ASI, Science Data Centre, via Galileo Galilei, 00044 Frascati, Italy
⁸ INAF – Roma Astronomical Observatory, via Frascati 33, 00040 Monteporzio Catone, Italy
⁹ INAF, IASF Bologna, via P. Gobetti 101, 40129 Bologna, Italy
¹⁰ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
¹¹ INAF – Padova Astronomical Observatory, vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹² INAF – Capodimonte Astronomical Observatory, Salita Moiariello 16, 80131 Napoli, Italy
¹³ ICRANET, Piazza della Republica 10, 65122 Pescara, Italy
¹⁴ Physics Department, University of Ferrara, via Saragat 1, Ferrara 44122, Italy
¹⁵ ARI, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
¹⁶ Departamento de Ciencias Fisicas, Universidad Andrés Bello, Av. República 252, Santiago, Chile
¹⁷ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18. 008 Granada, Spain
¹⁸ National Astronomical Observatories, CAS – 100012 Beijing, PR China
¹⁹ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
²⁰ NASA Marshall Space Flight Center, Huntsville, Alabama 35805, USA
²¹ Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, 277-8583 Chiba, Japan
²² European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
²³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
²⁴ INAF, IASF Milano, via E. Bassini 15, 20133 Milano, Italy
²⁵ Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
²⁶ National Astronomical Observatory of Japan, Mitaka, 181-8588 Tokyo, Japan
²⁷ GEPI, Observatoire de Paris, CNRS, Univ. Paris Diderot, 5 Pl. Jules Janssen, 92190 Meudon, France

Received: 20 June 2012
Accepted: 28 September 2012

Abstract

Aims. The association of Type Ic supernovae (SNe) with long-duration gamma-ray bursts (GRBs) is well established. We endeavor, through accurate ground-based observational campaigns, to characterize these SNe at increasingly high redshifts.

Methods. We obtained a series of optical photometric and spectroscopic observations of the Type Ic SN 2012bz associated with the Swift long-duration GRB 120422A (redshift z = 0.283) using the 3.6-m TNG and the 8.2-m VLT telescopes during the time interval between 4 and 36 days after the burst.

Results. The peak times of the light curves of SN 2012bz in various optical filters differ, with the B-band and i’-band light curves reaching maximum at 9 ± 4 and 23 ± 3 rest-frame days, respectively. The bolometric light curve has been derived from individual bands photometric measurements, but no correction for the unknown contribution in the near-infrared (probably around 10–15%) has been applied. Therefore, the present light curve should be considered as a lower limit to the actual UV-optical-IR bolometric light curve. This pseudo-bolometric curve reaches its maximum (M_bol =  −18.56 ± 0.06) at 13 ± 1 rest-frame days; it is similar in shape and luminosity to the bolometric light curves of the SNe associated with z < 0.2 GRBs and more luminous than those of SNe associated with X-ray flashes (XRFs). A comparison with the model generated for the bolometric light curve of SN 2003dh suggests that SN 2012bz produced only about 15% less ⁵⁶Ni than SN 2003dh, about 0.35   M_⊙. Similarly the VLT spectra of SN 2012bz, after correction for Galactic extinction and for the contribution of the host galaxy, suggest comparable explosion parameters with those observed in SN 2003dh (E_K ~ 3.5 × 10⁵² erg, M_ej ~ 7   M_⊙) and a similar progenitor mass (~25–40 M_⊙). GRB 120422A is consistent with the E_peak − E_iso and the E_X,iso − E_γ,iso − E_peak relations. GRB 120422A / SN 2012bz shows the GRB-SN connection at the highest redshift so far accurately monitored both photometrically and spectroscopically.