Multi-wavelength Emissions From Optical Transient AT2018cow And Progenitor Research

Due to the continuous upgrading of observation equipment and the operation of a new generation of sky survey projects(such as Pan-STARRS,PTF,ASSA-SN and ZTF,etc.),a large number of rare and fast evolving optical transients(Fast Optical Transient;FOT)have been detected in recent years,of which AT2018cow is one of the most representative transients.AT2018cow adopts a distance of 60 Mpc which makes it easy to be detected,so that people can obtain a wealth of multi-wavelength observation information.Its early spectrum shows remarkable blue colors,indicating higher temperature and peak luminosity,and the evolution of its light curve is extremely fast.These characteristics make it significantly different from typical core-collapse supernovae and thermonuclear explosion supernovae,which may imply a new astrophysical origin.On the one hand,we use the energy injection from the neutron star(NS)wind model to explain the optical emission of AT2018cow,which shows that under the con-tinuous energy supply of a millisecond magnetar,the thermal emission of an explosive ejecta with a mass of about 0.02M? can well match the results of optical observa-tions.On the other hand,we fit the radio afterglow of AT2018cow with shock-driven model.The parameters we limited with radio afte rglow,the ejecta mass and energy injection,,are highly consistent with the results we got from the optical emssion,which fully demonstrates self-consistent and feasibility of our model.At the same time,the radio afterglow fitting also shows this transient should occur in a pulsar wind environment.These results provide us with important clues for our understanding of the origin of fast-evolving optical transients represented by AT2018cow.First,the astrophysical processes that may result in the explosion of neutron stars and low-mass ejecta may include supernova explosions from ultra-stripped supernovae,double NS mergers,double white dwarf mergers,and accretion-induced collapse of white dwarfs.Among them,the last three processes are more likely to evolute into NS with the properties of millisecond magnetars.And the pulsar wind environment created before the explosion means the progenitor is likely to contain a massive star,so the accretion-induced collapse of the white dwarf becomes the most likely progenitor.Under the framework of this model,the interaction between the millisecond magnetar wind and the massive companion star can also help understand the hard X-ray radiation characteristics of AT2018cow.