Nuclear Dominated Accretion Flows in Two Dimensions. II. Ejecta dynamics and nucleosynthesis for CO and ONe white dwarfs. (arXiv:1905.06343v1 [astro-ph.HE])

Nuclear Dominated Accretion Flows in Two Dimensions. II. Ejecta dynamics and nucleosynthesis for CO and ONe white dwarfs. (arXiv:1905.06343v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Fernandez_R/0/1/0/all/0/1">Rodrigo Fern&#xe1;ndez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Margalit_B/0/1/0/all/0/1">Ben Margalit</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Metzger_B/0/1/0/all/0/1">Brian D. Metzger</a>

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 $19$-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 $10^2-10^4$ km s$^{-1}$. The outflow composition is mostly that of
the initial white dwarf, with burning products mixed in at the $lesssim
10-30%$ level by mass, including up to $sim 10^{-2}M_odot$ of ${}^{56}$Ni.
These heavier elements (plus ${}^{4}$He) are ejected within $lesssim 40^circ$
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 ($sim $ 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 $sim
10^{47}-10^{50}$ erg s$^{-1}$ and peak durations of up to several minutes,
possibly accounting for events like CDF-S XT2.

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 $19$-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 $10^2-10^4$ km s$^{-1}$. The outflow composition is mostly that of
the initial white dwarf, with burning products mixed in at the $lesssim
10-30%$ level by mass, including up to $sim 10^{-2}M_odot$ of ${}^{56}$Ni.
These heavier elements (plus ${}^{4}$He) are ejected within $lesssim 40^circ$
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 ($sim $ 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 $sim
10^{47}-10^{50}$ erg s$^{-1}$ and peak durations of up to several minutes,
possibly accounting for events like CDF-S XT2.

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