Double explosions and jet formation in GRB-supernova progenitors

TL;DR

This paper explores how a secondary relativistic outflow driven by a GRB central engine interacts with the supernova envelope, potentially forming highly collimated jets due to instabilities in steep density gradients.

Contribution

It introduces a model for jet formation via instabilities in the secondary GRB shock propagating through the supernova envelope, highlighting conditions for jet collimation.

Findings

Steep density gradients ( ho ~ r^{- extomega} with extomega > 4) favor jet formation.

Secondary shocks can become unstable and form collimated jets under certain conditions.

Non-spherical initial conditions influence outflow morphology.

Abstract

Progenitors of long GRBs, and core-collapse supernovae in general, may have two separate mechanisms driving the outflows: quasi-isotropic neutrino-driven supernova explosions followed by a highly collimated relativistic outflow driven by the GRB central engine, a black hole or a magnetar. We consider the dynamics of the second GRB-driven explosion propagating through expanding envelope generated by the passage of the primary supernova shock. Beyond the central core, in the region of steep density gradient created by the SN shock breakout, the accelerating secondary quasi-spherical GRB shock become unstable to corrugation and under certain conditions may form a highly collimated jet, a "chimney", when a flow expands almost exclusively along a nearly cylindrically collimated channel. Thus, weakly non-spherical driving and/or non-spherical initial conditions of the wind cavity may produce highly non-spherical, jetted outflows. For a constant luminosity GRB central engine, this occurs for density gradient in the envelope \rho ~ r^{-\omega} steeper than \omega >4.