A Diagnostic Method for Proto-Neutron Star Magnetic Fields by Supernova Fallback Neutrinos
Abstract
Young isolated neutron stars exhibit a wide range of magnetic field strengths. To understand the origin of this diversity, it is important to observationally constrain magnetic fields during the proto-neutron star (PNS) phase. We propose a novel diagnostic of PNS magnetic fields using neutrinos associated with supernova fallback. By performing one-dimensional general-relativistic magnetohydrodynamic simulations of the supernova fallback onto a magnetized PNS, we investigate how the energy spectra of the fallback neutrinos depend on the PNS magnetic field strength and the fallback accretion rate. We find that stronger magnetic fields and lower accretion rates produce softer spectra because the fallback neutrinos are emitted mainly near the magnetospheric radius, which becomes larger under these conditions. To quantify this spectral softening, we define a hardness ratio based on event rates above and below 30 MeV and introduce a hardness-event-rate diagram. Using this diagram, we identify the parameter region in which our diagnostic is applicable. Its applicability depends on the PNS magnetic field strength, fallback accretion rate, onset time of the fallback phase, and neutrino mass ordering. We also investigate the dependence on the PNS radius and find that a larger radius produces softer spectra, indicating a degeneracy between the magnetic field and PNS compactness. An independent constraint on the PNS compactness would therefore enable us to better constrain the magnetic field. These results suggest that future multimessenger observations of galactic supernovae can provide a new window into the NS diversity.
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BibTeX
@misc{inoue2026diagnostic,
title = {{A Diagnostic Method for Proto-Neutron Star Magnetic Fields by Supernova Fallback Neutrinos}},
author = {Akihiro Inoue and Yudai Suwa and Ryuichiro Akaho and Shinsuke Takasao and Kazumi Kashiyama and Hiroyuki R. Takahashi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28057},
eprint = {2609.28057},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28057},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A Diagnostic Method for Proto-Neutron Star Magnetic Fields by Supernova Fallback Neutrinos
AU - Akihiro Inoue
AU - Yudai Suwa
AU - Ryuichiro Akaho
AU - Shinsuke Takasao
AU - Kazumi Kashiyama
AU - Hiroyuki R. Takahashi
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.28057
UR - https://arxiv.org/abs/2609.28057
AB - Young isolated neutron stars exhibit a wide range of magnetic field strengths. To understand the origin of this diversity, it is important to observationally constrain magnetic fields during the proto-neutron star (PNS) phase. We propose a novel diagnostic of PNS magnetic fields using neutrinos associated with supernova fallback. By performing one-dimensional general-relativistic magnetohydrodynamic simulations of the supernova fallback onto a magnetized PNS, we investigate how the energy spectra of the fallback neutrinos depend on the PNS magnetic field strength and the fallback accretion rate. We find that stronger magnetic fields and lower accretion rates produce softer spectra because the fallback neutrinos are emitted mainly near the magnetospheric radius, which becomes larger under these conditions. To quantify this spectral softening, we define a hardness ratio based on event rates above and below 30 MeV and introduce a hardness-event-rate diagram. Using this diagram, we identify the parameter region in which our diagnostic is applicable. Its applicability depends on the PNS magnetic field strength, fallback accretion rate, onset time of the fallback phase, and neutrino mass ordering. We also investigate the dependence on the PNS radius and find that a larger radius produces softer spectra, indicating a degeneracy between the magnetic field and PNS compactness. An independent constraint on the PNS compactness would therefore enable us to better constrain the magnetic field. These results suggest that future multimessenger observations of galactic supernovae can provide a new window into the NS diversity.
ER -