arXiv subjects

Takumi Shimasue

Publications and source records attributed to Takumi Shimasue.

4 recordsLinked to original sources

arXiv2026

A Log-Uniform Initial Magnetic Field Distribution Explains Pulsar and Magnetar Populations through Magnetic Inclination Alignment

The origin of the gap in the observed magnetic field distribution between pulsars and magnetars raises a challenge to understanding these populations within a unified framework. We analytically show that the gap can be naturally explained by the alignment of the magnetic inclination angle between the magnetic and spin axes. Based on coupled evolution of spin-down and magnetic inclination angle in the plasma-filled magnetosphere, the alignment timescale follows $τ_α\propto B^{-2}$. Thus, strongly magnetized neutron stars including high-$B$ pulsars and magnetars align more rapidly than pulsars with $10^{12}\,\mathrm{G}$, reducing their beaming fraction and thereby suppressing their observed numbers. However, magnetars are primarily identified through X-ray activity and are therefore relatively less affected by beaming. Taking into account both beaming fraction and luminosity corrections, we reconstruct the initial magnetic field distribution from the observed distribution. We show that pulsars and magnetars do not dictate intrinsically distinct initial distributions, but can instead be understood within a single continuous initial magnetic field distribution, such as a log-uniform distribution.

astro-ph.HE↗

arXiv2026

Constraining the Pulsar Beaming Fraction with TeV-Selected Galactic Pulsar Wind Nebulae and unidentified TeV Sources

The pulsar beaming fraction is a fundamental quantity for connecting the observed pulsar population to the intrinsic Galactic population and for constraining pulsar emission geometry. In this study, we estimate the beaming fraction in each observational band (radio, $γ$-ray, and X-ray) and for each TeV survey (H.E.S.S., HAWC, and LHAASO) using TeV-selected pulsar wind nebulae (PWNe) and unidentified (Unid) TeV sources, assuming that the TeV emission from PWNe is approximately isotropic and that Unid sources are PWNe powered by pulsars whose beams do not intersect our line of sight. Within each survey, the inferred beaming fractions $\sim 0.1-0.3$ are comparable across bands. In contrast, the values differ by more than a factor of two between H.E.S.S. and HAWC/LHAASO. This discrepancy likely reflects survey-dependent selection effects, including differences in angular resolution and energy range, and is also consistent with the possibility that HAWC/LHAASO selected samples preferentially include older pulsars associated with more extended PWNe than those in the H.E.S.S. sample. We further show that the inferred beaming fractions can be reproduced within a unified framework using a time-dependent opening angle, and that this framework remains compatible with the statistical properties of the observed pulsar population.

astro-ph.HE↗

arXiv2026

Two unseen massive white dwarf candidates in close binaries

We report the discovery of two binary systems, each consisting of a slightly bloated G-type main-sequence star and an unseen companion, identified through photometric data from TESS and radial velocity variation from Gaia. High-resolution spectroscopy confirms orbital periods of 1.37 and 2 .67 d with circular orbits. The visible components have masses of $\sim$0.9--1.0$\,M_\odot$, while the minimum masses of the unseen companions are $1.078^{+0.058}_{-0.060}\, M_\odot$ and $0.943^{+0.048}_{-0.049}\, M_\odot$, respectively. Assuming tidal synchronization, we estimate the companion masses to be $1.13^{+0.11}_{-0.08} M_\odot$ and $1.05^{+0.15}_{-0.10} M_\odot$. The absence of detectable spectral features from the companions rules out main-sequence stars of these masses, suggesting that the unseen companions are likely O/Ne or C/O massive white dwarfs. The short orbital periods imply that these systems are post-common envelope binaries. Their subsequent evolution is uncertain, with possible outcomes including cataclysmic variables, Type Ia supernovae, or accretion-induced collapse, depending on the nature of future mass transfer.

astro-ph.SR↗

arXiv2023

Line-of-sight structure of troughs identified in Subaru Hyper Suprime-Cam Year 3 weak lensing mass maps

We perform the weak lensing mass mapping analysis to identify troughs, which are defined as local minima in the mass map. Since weak lensing probes projected matter along the line-of-sight, these troughs can be produced by single voids or multiple voids projected along the line-of-sight. To scrutinise the origins of the weak lensing troughs, we systematically investigate the line-of-sight structure of troughs selected from the latest Subaru Hyper Suprime-Cam (HSC) Year 3 weak lensing data covering $433.48 \, \mathrm{deg}^2$. From a curved sky mass map constructed with the HSC data, we identify 15 troughs with the signal-to-noise ratio higher than $5.7$ and address their line-of-sight density structure utilizing redshift distributions of two galaxy samples, photometric luminous red galaxies observed by HSC and spectroscopic galaxies detected by Baryon Oscillation Spectroscopic Survey. While most of weak lensing signals due to the troughs are explained by multiple voids aligned along the line-of-sight, we find that two of the 15 troughs potentially originate from single voids at redshift $\sim 0.3$. The single void interpretation appears to be consistent with our three-dimensional mass mapping analysis. We argue that single voids can indeed reproduce observed weak lensing signals at the troughs if these voids are not spherical but are highly elongated along the line-of-sight direction.

astro-ph.CO↗