The Emission Source of Supernova ASASSN-15nx with a Prolonged Linear Light Curve

Abstract

An analysis of the spectra for the anomalous supernova ASASSN-15nx with a linear light curve has ruled out the emission mechanisms through radioactivity and shock interaction with circumstellar gas. An alternative mechanism for the emission of ASASSN-15nx based on the interaction of a rotating neutron star magnetosphere with gravitationally bound ejecta material is proposed. In the regime of stationary accretion the neutron star rotation frequency and the rotational energy losses decrease exponentially with time, which can explain the linearity of the light curve. Modeling of the light curve at the initial stage of the luminosity rise in combination with the expansion velocity suggest a low ejecta mass, ~1 M_⨀. The shape of the [O I] 6300, 6364 Å doublet profile points to asphericity of the oxygen distribution, which, in turn, provides evidence for a highly aspherical explosion.