A fallback accretion model for the unusual type II-P supernova iPTF14hls.

The Intermediate Palomar Transient Factory reported the discovery of an unusual type II-P supernova iPTF14hls. Instead of a ~ 100-day plateau as observed for ordinary type II-P supernovae (SNe), the light curve of iPTF14hls has at least five distinct peaks. The effective temperature of iPTF14hls is roughly constant at 5000-6000K . The very slow evolution of the optical spectra, combined with the duration of one individual peak in the light curve, implies a massive ejecta. In this paper we propose that the multi-peaked light curve of iPTF14hls is a result of intermittent fallback accretion. Detailed modeling indicates that the total fallback mass is ~0.2M_sun, with an ejecta mass M_{ej}=21M_sun. We find the third peak of the light curve cannot be well fit by the fallback model, indicating that there could be some extra rapid energy injection. We suggest that this extra energy injection may be a result of a magnetic outburst if the central object is a neutron star. It is found that this burst lasted for ~20 days with a total burst energy 3.9\times 10^{48} erg . The above results indicate that the progenitor of iPTF14hls could be a massive red supergiant.