Study On Mergernovae And Superluminous Supernovae Under Central Engine Model

Typical supernovae and kilonovae are suggested to be powered by radioactive decay.Usually,the peak luminosity is limited by the heating rate of radioactive decay,which is decided by the ejecta mass and the amount of radioactive elements.Besides radioactive decay,the central engine may also play a significant role.A rapidly spinning magnetar as a central engine would make mergernovae and Superluminous Supernovae(SLSNe)become more luminous than kilonovae and typical supernovae.Historically,millisecond magnetar has already been suggested as the central engine of gamma ray burst(GRB).A long-lived magnetar is very helpful to explain the plateaus and flares discovered in afterglow emission.According to the duration of prompt emission,GRBs can be divided into long GRBs and short GRBs.Long GRBs are widely believed to be connected with massive star collapses,but short GRBs may originate from double compact star mergers.GRB 111209A/SN 2011kl is the first discovered GRB-SLSN association.The association of GRB 111209A/SN 2011kl connects the studys of GRBs and SLSNe.In 2017,the detection of gravitation wave(GW)signal GW 170817 directly verified that short GRBs could come from double neutron star mergers.Besides short GRBs,mergernovae formed after double neutron star mergers could also be the counterparts of GWs.Due to quasi-isotropic radiation and a higher luminosity compared with kilonovae,mergernovae are considered as the most promising electromag-netic counterparts of GWs.As an uniform central engine,a magnetar engine connects the researches of GRBs,mergernoave and SLSNe.Therefore,starting from GRB theory,we would mainly explore the application of magnetar model in mergernovae and SLSNe.Based on magnetar model,our works are at four aspects.(1)Double neutron star merger rate can be estimated from mergernova survey,which could be a guide for GW detection.As first attempt,we find several mergernova candidates in PS1-MDS survey.(2)It needs a more efficient way to select mergernovae candidates from so many optical transients in universe.Due to the energy injection frorm the central magnetar,a shock forms inside the merger ejecta and moves forward.It will give a bright emission when the shock breakout.This shock breakout signal could be a precursor emission to select mergernova candidates.(3)Mergernovae as GW counterparts would help to the identification of GW signals.The detectio-n of GW 170817 gives the first chance to study double neutron star merger process in detail.Based on the difference of kilonovae and mergernorvae,we refit AT 2017gfo lightcurve using central engine model.We find that mergernova model powered by a central neutron star can self-consistently explain AT 2017gfo.The results show that the post-merger product is a long-lived massive neutron star,challenging most of the Equation of State(EoS)of neutron star at present.(4)Besides double NS mergers,we also try to find the differences and potential relations between the central engines of GRBs and SLSNe.Prelimina.ry results from statistical analysis show the difference of magnetic field strength between SLSN magnetars and GRB magnetars.By introducing flare-like energy injection,we fit the undulations on SN 2015bn lightcurve.It suggests that the central engine has long timescale activities.Compared with GRB flares,it seems that there is a kind of correlation between them.Although the field strength is different,SLSN magnetars and GRB magnetars share similar property in activities.Based on this,we try to understand the magnetar-driven explosion events in an uniform view.It is very meaningful to build an uniform magnetar model in future.