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 ≈ 10 3 s, during which the average mass accretion rate is ≈ 10 −4 M s −1 . We outline the possible diversity of CEJSNe by listing five other scenarios in addition to the polar CEJSN scenario.

Explosions Driven by the Coalescence of a Compact Object with the Core of a Massive-star Companion inside a Common Envelope: Circumstellar Properties, Light Curves, and Population Statistics

“…The resulting transient is described as a "common envelope jets supernova" by Soker et al (2019). One of the key points that Chevalier (2012) and Soker et al (2019) mention is that the distribution of common envelope ejecta is crucial in shaping the observed light curve (see Kleiser et al 2018, for a similar discussion in the context of rapidly-fading supernovae). Here, we pursue this line of examination.…”

“…MERGER-DRIVEN EXPLOSIONS 2.1. Inspiral, Merger, and Central Engine Following its inspiral through the common envelope, a compact object can tidally disrupt and merge with the helium core of the massive star (Zhang & Fryer 2001;Chevalier 2012;Soker & Gilkis 2018;Soker et al 2019). The disrupted material forms an accretion disk surrounding the now-central compact object.…”

AT 2018cow VLBI: no long-lived relativistic outflow

“…In fact, various authors have already suggested that there might be a jet in AT 2018cow (Kuin et al 2019;Margutti et al 2019;Perley et al 2019;Soker, Grichener & Gilkis 2019). Due to the similarities with GRB-SNe, an off-axis GRB event, with a relativistic jet not directed along the line of sight, is a possibility.…”

“…Alternatively, Soker et al (2019) interpret AT 2018cow as the result of a binary star where a neutron star inspirals into its red giant companion, accreting rapidly when it reaches the dense core. Jets are produced, which clear the polar regions of the supergiant, which then form the observed high-velocity material.…”

Nature of the unusual transient AT 2018cow from HI observations of its host galaxy

“…It has been shown that it could not have been powered by radioactive decay (Prentice et al 2018;Margutti et al 2019;Perley et al 2019). Several models have been proposed to explain the observed properties: a stellar collapse leading to the formation of a magnetar (Prentice et al 2018;Margutti et al 2019), a luminous blue variable exploding in a non-uniform circum-stellar medium (Rivera Sandoval et al 2018), a SN from a lowmass hydrogen-rich star, a failed SN from a blue supergiant (Margutti et al 2019), a tidal disruption event (TDE; Liu et al 2018;Kuin et al 2018;Perley et al 2019), a jet driven by an accreting neutron star colliding with a giant star (Soker et al 2019), or a merger of white dwarfs (Lyutikov & Toonen 2018). However, the constraints on the nature of this explosion set by the host galaxy properties have not been explored thoroughly.…”