A magnetar model for the hydrogen-rich super-luminous supernova iPTF14hls

Transient surveys have recently revealed the existence of H-rich super-luminous supernovae (SLSN; e. g., iPTF14hls, OGLE-SN14-073) that are characterized by an exceptionally high time-integrated bolometric luminosity, a sustained blue optical color, and Dopplerbroadened H I lines at all times. Here, I investigate the effect that a magnetar (with an initial rotational energy of 4 x 10(50) erg and field strength of 7 x 10(13) G) would have on the properties of a typical Type II supernova (SN) ejecta (mass of 13.35 M-circle dot, kinetic energy of 1 : 32 x 10(51) erg, 0.077 M-circle dot of 56Ni) produced by the terminal explosion of an H-rich blue supergiant star. I present a non-local thermodynamic equilibrium time-dependent radiative transfer simulation of the resulting photometric and spectroscopic evolution from 1 d until 600 d after explosion. With the magnetar power, the model luminosity and brightness are enhanced, the ejecta is hotter and more ionized everywhere, and the spectrum formation region is much more extended. This magnetar-powered SN ejecta reproduces most of the observed properties of SLSN iPTF14hls, including the sustained brightness of 18 mag in the R band, the blue optical color, and the broad H I lines for 600 d. The non-extreme magnetar properties, combined with the standard Type II SN ejecta properties, offer an interesting alternative to the pair-unstable super-massive star model recently proposed, which involves a highly energetic and super-massive ejecta. Hence, such Type II SLSNe may differ from standard Type II SNe exclusively through the influence of a magnetar.