Study Of The Energy Sources Of Superluminous Supernovae

Superluminous supernovae(SLSNe)are a new class of supernovae that were rec-ognized about a decade ago.Most SLSNe are 10 to 100 times more luminous than typical SN Ia.Due to their brightness,SLSNe could be a powerful probe of distant Universe.What powered such high luminosity transients is still unknown.This thesis mainly focuses on the theoretical aspects of the energy sources of SLSNe.Three en-ergy sources are mainly suggested to account for the huge luminosity of SLSNe,i.e.,radioactive decay(56Ni),the interaction between ejecta and dense circumstellar medi-um(CSM),and magnetar spin-down.Both observational and theoretical progress has been significant in the last decade.In chapter 1,we review the research progresses of SLSNe in both observational and theoretical aspects.In chapter 2,we collect 19 hydrogen-deficient SLSNe and fit their light curves,temperature evolution,and velocity evolution based on the magnetar-powered model.To obtain the best-fitting parameters,we incorporate the Markov Chain Monte Carlo approach.We obtain very good fits for seven events.We find that the initial periods(P0)and magnetic strength(Bp)of the magnetars supposed to power these SLSNe are in the range of?1.2-8.3 ms and?(0.2-8.8)×1014 G,respectively;the inferred masses of the ejecta of these SLSNe are between 1 and 27.6 M?.We also calculate the fraction of the initial rotational energy of the magnetars harbored in the centers of the remnants of these SLSNe that is converted to the kinetic energy of the ejecta and find that the fraction is?19-97%for different values of P0 and Bp,indicating that the acceleration effect cannot be neglected.Moreover,we find that the initial kinetic energies of most of these SLSNe are so small((?)2 × 1051 erg).These results can help clarify some important issues related to the energy-source mechanisms and explosion mechanisms and reveal the nature of SLSNe.In chapter 3,we investigate two hydrogen-poor SLSNe,iPTF1 5esb and iPTF13dcc,whose light curves(LCs)show significant deviation from the smooth rise and fall.The LC of iPTF 15esb exhibits two peaks and a post-peak plateau,and furthermore the late-time spectrum of iPTF 15esb shows a strong,broad Ha emission line.The early-time LC of iPTF13dcc shows a long-duration bump followed by the second peak.Here,we pro-pose an ejecta-circumstellar medium interaction model involving multiple shells/winds and use it to explain the LCs of iPTF15esb and iPTF 13dcc.We find that the theoretical LCs reproduced by this model can match observations of iPTF15esb and iPTF13dcc.Based on our results,we infer that the progenitors have undergone multiple violent mass-loss processes before the SN explosion.In addition,we find that the variation trend of our inferred densities of the shells is consistent with that predicted by the stel-lar mass-loss history before an SN explosion.Further investigations for other bumpy SLSNe/SNe would shed light on their nature and provide a probe for the mass-loss history of their progenitors.Recent wide-field surveys discovered new types of peculiar optical transients that showed diverse behaviors of the evolution of photospheric properties.In chapter 4,we develop a general theory of homologous explosions with constant opacity,paying special attention on the evolution of the photospheric radius R ph·We find that regard-less of the density distribution profile,R ph always increases early on and decreases at late times.This result does not depend on the radiation and cooling processes inside the ejecta.The general rising/falling behavior of Rph can be used to quickly diagnose whether the source originates from a supernova-like explosion.The shape of the Rph evolution curve depends on the density profile,so the observations may be used to di-rectly diagnose the density profile as well as the temperature profile of the ejecta.All the well-monitored supernovae show such a Rph rising/falling behavior,which is con-sistent with our theory.The recently discovered peculiar transient AT2018cow showed a continuous decay of Rph,which is disfavored to be of a supernova-like explosion ori-gin.Our result therefore supports the interpretation of this transient as a tidal disruption event.Both interaction-powered and magnetar-powered models can provide reasonable fits to most SLSNe LCs with a proper choice of the model parameters.However,there is not a definitive conclusion have been reached yet.We summarize our results and make a brief prospect in chapter 5.