Nuclear Burning in Collapsar Accretion Disks

Abstract

The core collapse of massive, rapidly-rotating stars are thought to be the progenitors of long-duration gamma-ray bursts (GRB) and their associated hyper-energetic supernovae (SNe). At early times after the collapse, relatively low angular momentum material from the infalling stellar envelope will circularize into an accretion disk located just outside the black hole horizon, resulting in high accretion rates necessary to power a GRB jet. Temperatures in the disk midplane at these small radii are sufficiently high to dissociate nuclei, while outflows from the disk can be neutron-rich and may synthesize r-process nuclei. However, at later times, and for high progenitor angular momentum, the outer layers of the stellar envelope can circularize at larger radii 10 7 cm, where nuclear reactions can take place in the disk midplane (e.g. 4 He + 16 O → 20 Ne + γ). Here we explore the effects of nuclear burning on collapsar accretion disks and their outflows by means of hydrodynamical α-viscosity torus simulations coupled to a 19-isotope nuclear reaction network, which are designed to mimic the late infall epochs in collapsar evolution when the viscous time of the torus has become comparable to the envelope fall-back time. Our results address several key questions, such as the conditions for quiescent burning and accretion versus detonation and the generation of 56 Ni in disk outflows, which we show could contribute significantly to powering GRB supernovae. Being located in the slowest, innermost layers of the ejecta, the latter could provide the radioactive heating source necessary to make the spectral signatures of r-process elements visible in late-time GRB-SNe spectra.

Viscous evolution of a massive disk surrounding stellar-mass black holes in full general relativity

“…This may indicate that the bulk of 56 Ni in this type of supernovae comes from the early ejecta [89], for which the driving mechanism is unsettled ( neutrino heating or magnetic pressure). It is also suggested that the detonation of the late-time accreted material can be an additional source of 56 Ni [90].…”

Possible post-kick jets in SN 1987A

“…There is an increasing recognition of the importance of post-explosion accretion disks that fall back material forms around the central NS or black hole, including outflows from the accretion disks (e.g., Akashi & Soker 2020;Liu et al 2020;Zenati et al 2020 for very recent papers). The jittering jets explosion mechanism that attributes the explosion itself to jets, accounts also for post-explosion jets.…”