Multipolar neutrino radiation in binary neutron star mergers: Angular structure, rotational variability, and implications for electron fraction
Abstract
The angular structure and temporal variability of neutrino emission from binary neutron star mergers are characterized using fully general-relativistic simulations with energy-integrated M1 neutrino transport across a representative set of equations of state, total masses and mass ratios. The main analysis is restricted to merger remnants that do not collapse to a black hole within the simulated time intervals. The angle-dependent neutrino energy flux is extracted on a spherical surface outside the remnant and decomposed into spherical harmonics to quantify its multipolar content and evolution. Following the initial post-merger transient, the neutrino radiation flux approaches an axisymmetric configuration dominated by a strong quadrupolar component, producing persistent polar flux enhancement and equatorial suppression due to torus shadowing. The dipolar contribution remains subdominant, indicating the absence of sustained one-sided emission. The degree of anisotropy increases with mass asymmetry and for softer equations of state, reflecting the compactness and morphology of the remnant--disk system. Superimposed on this time-averaged geometry, coherent azimuthal modulations associated with the m=1 mode are identified. The associated half frequency, fdom/2≃0.6--0.7 kHz, is compared with local rotation rates in the simulated remnant--disk systems, suggesting a possible dynamical association between the remnant structure and neutrino variability. Finally, we quantify how the same quadrupole-dominated radiation geometry induces a latitude-dependent equilibrium electron fraction. The polar material is driven close to the neutrino-equilibrium target, whereas equatorial material remains systematically more neutron rich and below equilibrium.
Versions
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BibTeX
@misc{cokluk2026multipolar,
title = {{Multipolar neutrino radiation in binary neutron star mergers: Angular structure, rotational variability, and implications for electron fraction}},
author = {Kutay Arınç Çokluk and Albino Perego and Federico Maria Guercilena and Kadri Yakut},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2608.16275},
eprint = {2608.16275},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.16275},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Multipolar neutrino radiation in binary neutron star mergers: Angular structure, rotational variability, and implications for electron fraction
AU - Kutay Arınç Çokluk
AU - Albino Perego
AU - Federico Maria Guercilena
AU - Kadri Yakut
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2608.16275
UR - https://arxiv.org/abs/2608.16275
AB - The angular structure and temporal variability of neutrino emission from binary neutron star mergers are characterized using fully general-relativistic simulations with energy-integrated M1 neutrino transport across a representative set of equations of state, total masses and mass ratios. The main analysis is restricted to merger remnants that do not collapse to a black hole within the simulated time intervals. The angle-dependent neutrino energy flux is extracted on a spherical surface outside the remnant and decomposed into spherical harmonics to quantify its multipolar content and evolution. Following the initial post-merger transient, the neutrino radiation flux approaches an axisymmetric configuration dominated by a strong quadrupolar component, producing persistent polar flux enhancement and equatorial suppression due to torus shadowing. The dipolar contribution remains subdominant, indicating the absence of sustained one-sided emission. The degree of anisotropy increases with mass asymmetry and for softer equations of state, reflecting the compactness and morphology of the remnant--disk system. Superimposed on this time-averaged geometry, coherent azimuthal modulations associated with the m=1 mode are identified. The associated half frequency, f_dom/2≃0.6--0.7 kHz, is compared with local rotation rates in the simulated remnant--disk systems, suggesting a possible dynamical association between the remnant structure and neutrino variability. Finally, we quantify how the same quadrupole-dominated radiation geometry induces a latitude-dependent equilibrium electron fraction. The polar material is driven close to the neutrino-equilibrium target, whereas equatorial material remains systematically more neutron rich and below equilibrium.
ER -