Simulations of Accretion Powered Supernovae in the Progenitors of Gamma-Ray Bursts

Abstract

Observational evidence suggests a link between long duration gamma ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically-symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in one spatial dimension and with rotation, an explicit shear viscosity, and convection in the mixing length theory approximation. Once the accretion flow becomes rotationally supported outside of the black hole, an accretion shock forms and traverses the stellar envelope. Energy is carried from the central geometrically thick accretion disk to the stellar envelope by convection. Energy losses through neutrino emission and nuclear photodisintegration are calculated but do not seem important following the rapid early drop of the accretion rate following circularization. We find that the shock velocity, energy, and unbound mass are sensitive to convective efficiency, effective viscosity, and initial stellar angular momentum. Our simulations show that given the appropriate combinations of stellar and physical parameters, explosions with energies ∼ 5 × 10 50 ergs, velocities ∼ 3000 km s −1 , and unbound material masses 6 M are possible in a rapidly rotating 16 M main sequence progenitor star. Further work is needed to constrain the values of these parameters, to identify the likely outcomes in more plausible and massive LRGB progenitors, and to explore nucleosynthetic implications.

Nuclear Burning in Collapsar Accretion Disks

“…They followed the evolution up to a few hundred seconds, and found the evolution of the accretion rate is consistent with the light curve evolution of long GRBs, and showed that a thick disk forms around the stellar black hole remnant. Lindner et al (2012) showed the kinetic energy exceeds ∼ 5 × 10 50 erg, and their estimates of the peak net outflow rate at a larger radius are comparable to our FLASH simulation. Although using similar tools (FLASH) and following the evolution for hundreds of seconds, these simulations did not include nucleosynthesis processes, which are the focus of the current work.…”

“…Zhang et al 2006 for a review), a cut-off in the feeding rate from the outer disk, due to a combination of disk winds and convection, offers a plausible explanation within our scenario. Lindner et al (2010) present a somewhat different physical mechanism for the rapid decay in accretion rate involving outwards propagation of the accretion shock through the progenitor envelope, while convection in the disk as a way to suppress the accretion rate has also been proposed previously (Quataert & Gruzinov 2000;Milosavljević et al 2012;Lindner et al 2012).…”

Delayed Energy Injection Model for Gamma-Ray Burst Afterglows

“…Models to explain the plateaus or bumps always involve in "finding" later energy sources which would dominate the later radiation. The Poynting-flux from magnetars (Metzger et al 2011;Dai & Liu 2012;Bernardini et al 2012) or BH accretion systems (Cannizzo et al 2011;Lindner et al 2012) can play this role. When the later reactivities of the central engines have to be considered, the later radiation may be modified in two ways: refreshing the external shock in the fireball frame or attributing the later light curve to the jet luminosity directly from central engine.…”

Confined Population Iii Enrichment and the Prospects for Prompt Second-Generation Star Formation

“…The stars with masses 140 − 260 M explode as pairinstability supernovae (PISNe), and even more massive stars can also directly collapse into a black hole. Stellar rotation introduces new effects and significant theoretical uncertainties, e.g., the stars might first form a central black hole and the subsequent accretion of the rotating stellar envelope onto the black hole might power an outflow that could produce an explosion (see, e.g., MacFadyen & Woosley 1999;MacFadyen et al 2001;Kohri et al 2005;Milosavljević et al 2012;Lindner et al 2012), with a peculiar nucleosynthetic imprint that can be sought in especially metal-poor stars (e.g., Iwamoto et al 2005).…”