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tokens: Bildsten 2010 ), we obtain ejecta mass , kinetic energy erg, magnetic flux density , rotation period ms. Here we have assumed an expansion velocity at peak of 5600 km s from the Fe ii velocity, and opacity . This simple model cannot reproduce the early peak, and therefore we fit only the later epochs; however, including all the epochs provides almost identical parameters. To reproduce the early peak in the magnetar scenario as well, we consider the early light curve as possibly produced by a magnetar-induced shock breakout (SBO), as described by Kasen et al. (2016) . Using the above derived parameters from the fit of the main peak with the magnetar model, we can derive the time of the SBO peak and its luminosity ( Kasen et al. 2016 , their Eqs. (26) and (27)). Both these values are off from what we actually observe in PTF11mnb; we obtained a peak epoch for the SBO of 83 days, with luminosity erg. Therefore, we do not favor a magnetar as the energy source for the early peak. Since a magnetar-induced SBO model does not fit the early light curve of PTF11mnb, whereas the early peak was nicely fit by a Ni decay model (see Sect. 6.2 ), here we also consider a hybrid model in which the first peak is due to a regular SN explosion powered by radioactivity, while the main peak is powered by a magnetar. It is indeed possible to fit the bolometric light curve with a simple Arnett model ( Arnett 1982 ) representing the radioactive component, plus a magnetar model ( Kasen Bildsten 2010 ) that injects energy in the ejecta starting a few days after explosion. This is illustrated in Fig. 11 , where the Arnett model is plotted as a dotted blue line and the magnetar model by a dashed black line. The sum of the two models, shown as a dashed red line, fit the bolometric light curve well. The magnetar injection of energy would have to start after 18 days from the SN explosion, otherwise it is not possible to reproduce both peaks simultaneously. In such a scenario, the SN explosion is characterized by , erg, , and the magnetar by and ms. The magnetar parameters in the hybrid model are different from those of the magnetar-only model previously described. Despite the nice fit of this hybrid model to the bolometric light curve, we still favor a progenitor scenario with the explosion of a massive star and a double-peaked Ni distribution because such a scenario requires a single source of energy and fewer parameters and, in particular, it naturally fits the post main-peak light curve. 6.4. Early light-curve modeling The early -band light curve of PTF11mnb appears rather flat in the first three epochs, which occur merely 4 d after the last non-detection. To reproduce this early emission, we adopted the model by Piro Nakar (2013) for the shock breakout cooling tail, assuming and kinetic energy and ejecta mass from the hydrodynamical fit to the bolometric light curve. We solved for the explosion epoch and for the progenitor radius, obtaining a radius of 90–105 and an