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 an ∼100 day plateau as observed for ordinary type II-P supernovae, the light curve of iPTF14hls has at least five distinct peaks, followed by a steep decline at ∼1000 days since discovery. Until 500 days since discovery, the effective temperature of iPTF14hls is roughly constant at 5000-6000 K. In this paper, we propose that iPTF14hls is likely powered by intermittent fallback accretion. It is found that the light curve of iPTF14hls can be well fit by the usual t accretion law until ∼1000 days post discovery when the light curve transitions to a steep decline. To account for this steep decline, we suggest a power-law density profile for the late accreted material, rather than the constant profile as appropriated for the t accretion law. Detailed modeling indicates that the total fallback mass is ∼0.2 M , with an ejecta mass M ≃ 21 M . 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. These results indicate that the progenitor of iPTF14hls could be a massive red supergiant.© 2018. The American Astronomical Society. All rights reserved.We thank Iair Arcavi and Jesper Sollerman for providing us with the observational data. We also thank the anonymous referee for helpful comments. This work is supported by the National Program on Key Research and Development Project of China (Grant Nos. 2016YFA0400801 and 2017YFA0402600), National Basic Research Program of China (>973> Program, Grant No. 2014CB845800) and the National Natural Science Foundation of China (Grant Nos. 11573014, 11533033, 11673006). X. Wang is supported by the National Natural Science Foundation of China (NSFC grants 11325313 and 11633002), and the National Program on Key Research and Development Project (Grant No. 2016YFA0400803). S. Q. W. and L. D. L. are also supported by the China Scholarship Program to conduct research at U.C. Berkeley and UNLV, respectively