paper

Nuclear Dominated Accretion Flows in Two Dimensions. II. Ejecta dynamics and nucleosynthesis for CO and ONe white dwarfs

arXiv:1905.06343 · doi:10.1093/mnras/stz1701

Abstract

We study mass ejection from accretion disks formed in the merger of a white dwarf with a neutron star or black hole. These disks are mostly radiatively-inefficient and support nuclear fusion reactions, with ensuing outflows and electromagnetic transients. Here we perform time-dependent, axisymmetric hydrodynamic simulations of these disks including a physical equation of state, viscous angular momentum transport, a coupled -isotope nuclear network, and self-gravity. We find no detonations in any of the configurations studied. Our global models extend from the central object to radii much larger than the disk. We evolve these global models for several orbits, as well as alternate versions with an excised inner boundary to much longer times. We obtain robust outflows, with a broad velocity distribution in the range km s. The outflow composition is mostly that of the initial white dwarf, with burning products mixed in at the level by mass, including up to of Ni. These heavier elements (plus He) are ejected within of the rotation axis, and should have higher average velocities than the lighter elements that make up the white dwarf. These results are in broad agreement with previous one- and two-dimensional studies, and point to these systems as progenitors of rapidly-rising ( few day) transients. If accretion onto the central BH/NS powers a relativistic jet, these events could be accompanied by high energy transients with peak luminosities erg s and peak durations of up to several minutes, possibly accounting for events like CDF-S XT2.

Accepted by MNRAS. Updated Fig 10 (velocity distribution for NS or BH) and added new Fig 15 (comparison with exploding model from Paper I). Minor changes otherwise

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