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

Aims. The association of Type Ic supernovae (SNe) with long-duration gamma-ray bursts (GRBs) is well established. We endeavor, through\naccurate ground-based observational campaigns, to characterize these SNe at increasingly high redshifts.\nMethods. We obtained a series of optical photometric and spectroscopic observations of the Type Ic SN 2012bz associated with the Swift long-\nduration 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\nafter the burst.\nResults. 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\nmaximum at 9 ± 4 and 23 ± 3 rest-frame days, respectively. The bolometric light curve has been derived from individual bands photometric\nmeasurements, but no correction for the unknown contribution in the near-infrared (probably around 10­-15%) has been applied. Therefore, the\npresent light curve should be considered as a lower limit to the actual UV-optical-IR bolometric light curve. This pseudo-bolometric curve reaches\nits maximum (Mbol = -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\nassociated with z < 0.2 GRBs and more luminous than those of SNe associated with X-ray flashes (XRFs). A comparison with the model generated\nfor the bolometric light curve of SN 2003dh suggests that SN 2012bz produced only about 15% less 56 Ni than SN 2003dh, about 0.35 M . Similarly\nthe VLT spectra of SN 2012bz, after correction for Galactic extinction and for the contribution of the host galaxy, suggest comparable explosion\nparameters with those observed in SN 2003dh (EK 3.5 × 1052 erg, Mej 7 M ) and a similar progenitor mass (25­40 M ). GRB 120422A is\nconsistent with the Epeak - Eiso and the EX,iso - E,iso - Epeak relations. GRB 120422A / SN 2012bz shows the GRB-SN connection at the highest\nredshift so far accurately monitored both photometrically and spectroscopically.