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Neutrino absorption and other physics dependencies in neutrino-cooled black hole accretion discs

par Just, Oliver;Goriely, Stéphane ;Janka, Hans-Thomas;Nagataki, S;Bauswein, Andreas
Référence Monthly notices of the Royal Astronomical Society, 509, page (1377)
Publication Publié, 2021-10-08

Article révisé par les pairs

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Résumé :

Black hole (BH) accretion discs foed in compact-object mergers or collapsars may be major sites of the rapid-neutron-capture (r-)process, but the conditions deteining the electron fraction (Ye) remain uncertain given the complexity of neutrino transfer and angular-momentum transport. After discussing relevant weak-interaction regimes, we study the role of neutrino absorption for shaping Ye using an extensive set of silations perfoed with two-moment neutrino transport and again without neutrino absorption. We vary the torus mass, BH mass and spin, and examine the impact of rest-mass and weak-magnetism corrections in the neutrino rates. We also test the dependence on the angular-momentum transport treatment by comparing axisymmetric models using the standard α-viscosity with viscous models assuming constant viscous length-scales (lt) and 3D magnetohydrodynamic (MHD) silations. Finally, we discuss the nucleosynthesis yields and basic kilonova properties. We find that absorption pushes Ye towards 0.5 outside the torus, while inside increasing the equilibrium value $Y_math{ e}{math{eq}}$ by 0.05-0.2. Correspondingly, a substantial ejecta fraction is pushed above Ye = 0.25, leading to a reduced lanthanide fraction and a brighter, earlier, and bluer kilonova than without absorption. More compact tori with higher neutrino optical depth, τ, tend to have lower $Y_math{ e}{math{eq}}$ up to τ 1-10, above which absorption becomes strong enough to reverse this trend. Disc ejecta are less (more) neutron rich when employing an lt = const. viscosity (MHD treatment). The solar-like abundance pattern found for our MHD model marginally supports collapsar discs as major r-process sites, although a strong r-process may be limited to phases of high mass-infall rates, $dot{M}, raise0.14em>lower0.28em, 2times 10{-2}$ M s-1.