Failed Collapsar Jets to Explain Low Luminosity GRB Properties

Abstract

Using the collapsar scenario for long GRBs [1], we present series of numerical simulations to investigate properties of expanding jets, driven by engines deploying the same total energy (10 52 erg), differently. We include a wide range of engine durations (T inj ), from 0.1 to 100 sec, as well as different initial opening angles (θ 0 ) for the deployed energy. We employ an AMR 2D special relativistic hydrodynamical code, using a 25 solar mass Wolf-Rayet star as the progenitor [2]. We analyze the effect of the engine duration on the jet's hydrodynamic properties, and discuss the implications on GRB and SN emissions. Our results show that the expanding jet's hydrodynamical properties significantly differ, in particular outflow collimation and relativistic acceleration. The implication of this is that brief engines (with T inj < T breakout , either due to a short T inj or to a large θ 0 ) represent excellent systems to explain the debated low-luminosity GRBs (llGRBs), displaying two of llGRBs peculiar features: i) the estimated llGRBs rate at least about 100 times higher than that of GRBs [3,4,5], and ii) potentially energetic SN emission [6]. We find that these two features only arise from brief engines. The conclusion is that brief engines dominate collapsars, at least at low redshift.