The optical transients powered by millisecond magnetars

It is believed that magnetars play an important role in various astrophysical transients from gamma-ray bursts (GRBs) to superluminous supernovae (SLSNe). In this talk I will first discuss the reverse shock emission powered by magnetars following the mergers of double neutron stars. It is found that a significant fraction of the reverse shock emission is in the form of high-energy photons. Then I will move on to discuss magnetar-powered SLSNe. We have developed a model to account for the dynamics of the ejecta and their transition to the nebular phase. To our surprise, we found that SLSNe may provide insight into the formation of strange stars because the needed rotational energy is in excess of the commonly accepted upper limits of a normal neutron star.