The Fast Flavor Instability in Hypermassive Neutron Star Disk Outflows

Abstract

We examine the effect of neutrino flavor transformation by the fast flavor instability (FFI) on long-term mass ejection from accretion disks formed after neutron star mergers. Neutrino emission and absorption in the disk set the composition of the disk ejecta, which subsequently undergoes $r$-process nucleosynthesis upon expansion and cooling. Here we perform 28 time-dependent, axisymmetric, viscous-hydrodynamic simulations of accretion disks around hypermassive neutron stars (HMNSs) of variable lifetime, using a 3-species neutrino leakage scheme for emission and an annular-lightbulb scheme for absorption. We include neutrino flavor transformation due the FFI in a parametric way, by modifying the absorbed neutrino fluxes and temperatures, allowing for flavor mixing at various levels of flavor equilibration, and also in a way that aims to respect the lepton-number preserving symmetry of the neutrino self-interaction Hamiltonian. We find that for a promptly-formed black hole (BH), the FFI lowers the average electron fraction of the disk outflow due to a decrease in neutrino absorption, driven primarily by a drop in electron neutrino/antineutrino flux upon flavor mixing. For a long-lived HMNS, the disk emits more heavy lepton neutrinos and reabsorbs more electron neutrinos than for a BH, with a smaller drop in flux compensated by a higher neutrino temperature upon flavor mixing. The resulting outflow has a broader electron fraction distribution, a more proton-rich peak, and undergoes stronger radiative driving. Disks with intermediate HMNS lifetimes show results that fall in between these two limits. In most cases, the impact of the FFI on the outflow is moderate, with changes in mass ejection, average velocity, and average electron fraction of order $\sim 10\%$, and changes in the lanthanide/actinide mass fraction of up to a factor $\sim 2$.

Accepted by PRD. Added appendix with derivation of asymmetric oscillation coefficients, minor changes otherwise

References in corpus (25)

• Multi-messenger Observations of a Binary Neutron Star Merger
• Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. II. UV, Optical, and Near-IR Light Curves and Comparison to Kilonova Models
• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• The Emergence of a Lanthanide-Rich Kilonova Following the Merger of Two Neutron Stars
• Neutrino-driven winds from neutron star merger remnants
• Modeling GW170817 based on numerical relativity and its implications
• Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817
• The Dynamics of Binary Neutron Star Mergers and of GW170817
• Full Transport Model of GW170817-Like Disk Produces a Blue Kilonova
• SkyNet: A modular nuclear reaction network library
• Outflows from accretion disks formed in neutron star mergers: effect of black hole spin
• First 100 ms of a long-lived magnetized neutron star formed in a binary neutron star merger
• Imprints of neutrino-pair flavor conversions on nucleosynthesis in ejecta from neutron-star merger remnants
• Post-merger Mass Ejection of Low-mass Binary Neutron Stars
• Fast flavor oscillations in dense neutrino media with collisions
• Collective fast neutrino flavor conversions in a 1D box: Initial condition and long-term evolution
• Neutrino Flavor Conversions in High-Density Astrophysical and Cosmological Environments
• The landscape of disk outflows from black hole - neutron star mergers
• Fast Neutrino Flavor Conversion at Late Time
• Long-term evolution of neutron-star merger remnants in general relativistic resistive-magnetohydrodynamics with a mean-field dynamo term
• Jet Launching from Binary Neutron Star Mergers: Incorporating Neutrino Transport and Magnetic Fields
• On accretion disks formed in MHD simulations of black hole-neutron star mergers with accurate microphysics
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• Long-term 3D-MHD Simulations of Black Hole Accretion Disks formed in Neutron Star Mergers

Cited by in corpus (10)

• Asymptotic states of fast neutrino-flavor conversions in the three-flavor framework
• Quasi-steady evolution of fast neutrino-flavor conversions
• Flavor Equilibration of Supernova Neutrinos: Exploring the Dynamics of Slow Modes
• Predicting the outcome of collisional neutrino flavor conversion
• Many-Body Simulations of the Fast Flavor Instability
• Symmetry breaking due to multi-angle matter-neutrino resonance in neutron star merger remnants
• Impact of Neutrino Flavor Conversions on Neutron Star Merger Dynamics, Ejecta, Nucleosynthesis, and Multi-Messenger Signals
• Testing common approximations of neutrino fast flavor conversion
• Collapsar Disk Outflows III: Detectable Neutrino and Gravitational Wave Signatures
• Occurrence of fast neutrino flavor conversions in QCD phase-transition supernovae