Multiwavelength analysis of three supernovae associated with gamma-ray bursts observed by GROND

Context. After the discovery of the first connection between gamma-ray bursts (GRBs) and supernovae (SNe) almost two decades ago, tens of SN-like rebrightenings have been discovered and about seven solid associations have been spectroscopically confirmed to date. Aims. We determine the luminosity, evolution, and origin of three SN rebrightenings in GRB afterglow light curves at z similar to 0.5 along with accurate determinations of the host-galaxy extinction. We estimate physical parameters of the SN explosions, such as synthesised Ni-56 mass, ejecta mass, and kinetic energy. Methods. We employ GROND optical/NIR data and Swift X-ray/UV data to estimate the host-galaxy extinction by modelling the afterglow spectral energy distribution, to determine the SN luminosity and evolution, and to construct quasi-bolometric light curves. The latter are corrected for the contribution of the NIR-bands using data available in the literature and black-body fits. We employ Arnett's analytic approach to obtain the physical parameters of the explosion. Results. The SNe 2008hw, 2009nz, and 2010ma observed by GROND exhibit 0.80, 1.15, and 1.78 times the optical (r'-band) luminosity of SN 1998bw, respectively. While SN 2009nz exhibits an evolution similar to SN 1998bw, SNe 2008hw and 2010ma show earlier peak times. The quasi-bolometric light curves (340-2200 nm) confirm the large luminosity of SN 2010ma (1.4 x 10(43) erg s(-1)), while SNe 2008hw and 2009nz reached a peak luminosity closer to that of SN 1998bw. The modelling indicates in Ni-56 masses of around 0.4-0.5 M-circle dot. Conclusions. By means of a very comprehensive data set, we found that the luminosity and the Ni-56 mass of SNe 2008hw, 2009nz, and 2010ma resembles those of other known GRB-associated SNe. These findings strengthens previous claims of GRB-SNe being brighter than stripped-envelope SNe unaccompanied by GRBs.