2012A&A...547A..82M

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. We obtained a series of optical photometric and spectroscopic observations of the Type Ic SN2012bz associated with the Swift long-duration GRB120422A (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. The peak times of the light curves of SN2012bz 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 SN2003dh suggests that SN2012bz produced only about 15% less ⁵⁶Ni than SN2003dh, about 0.35M_☉. Similarly the VLT spectra of SN2012bz, after correction for Galactic extinction and for the contribution of the host galaxy, suggest comparable explosion parameters with those observed in SN2003dh (E_K∼3.5x10⁵²erg, M_ej∼7M_☉) and a similar progenitor mass (∼25-40M_☉). GRB120422A is consistent with the E_peak-E_iso and the E_X,iso-E_γ,iso-E_peak relations. GRB120422A/SN2012bz shows the GRB-SN connection at the highest redshift so far accurately monitored both photometrically and spectroscopically.