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arXiv · 2604.16187

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

Takumi Shimasue·Shota Kisaka·Aya Bamba·Shinpei Shibata
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Abstract

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, $\gamma$-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.

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Takumi Shimasue, Shota Kisaka, Aya Bamba, Shinpei Shibata. 2026-04-17. Constraining the Pulsar Beaming Fraction with TeV-Selected Galactic Pulsar Wind Nebulae and unidentified TeV Sources. https://arxiv.org/abs/2604.16187

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