Diversity of common envelope jets supernovae and the fast transient AT2018cow

Abstract

We propose a common-envelope jets supernova (CEJSN) scenario for the fast-rising blue optical transient AT2018cow. In a CEJSN a neutron star (NS) spirals-in inside the extended envelope of a massive giant star and enters the core. The NS accretes mass from the core through an accretion disc and launches jets. These jets explode the core and the envelope. In the specific polar CEJSN scenario that we propose here the jets clear the polar regions of the giant star before the NS enters the core. The jets that the NS launches after it enters the core expand almost freely along the polar directions that contain a small amount of mass. This, we suggest, explains the fast rise to maximum and the fast ejecta observed at early times of the enigmatic transient AT2018cow. The slower later time ejecta is the more massive equatorial outflow. We roughly estimate the accretion phase onto the NS during the explosion phase to last for a time of about 1000 seconds, during which the average mass accretion rate is about 0.0001 Mo/sec. We outline the possible diversity of CEJSNe by listing five other scenarios in addition to the polar CEJSN scenario.