Ultra-luminous X-ray pulsars as sources of TeV neutrinos

¹ Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, University of Tuebingen, Sand 1, 72076 Tübingen, Germany
² INAF – Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (LC), Italy
³ Faculty of Physics, University of Białystok, ul. K. Ciołkowskiego 1L, 15-245 Białystok, Poland
⁴ Dr. Karl Remeis Observatory, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany

^⋆ Corresponding author: ducci@astro.uni-tuebingen.de

Received: 21 April 2025
Accepted: 4 August 2025

Abstract

We explored the expected properties of the neutrino emission from accreting neutron stars in X-ray binaries using numerical simulations. The simulations are based on a model in which neutrinos are produced by the decay of charged pions and kaons, generated in inelastic collisions between protons accelerated up to TeV energies in the magnetosphere of a magnetized (B ∼ 10¹² G) neutron star and protons of the accretion disc. Our results show that this process can produce strong neutrino emission up to a few tens of TeV when the X-ray luminosity is above ∼10³⁹ erg s⁻¹, as in ultra-luminous X-ray (ULX) pulsars. We show that neutrinos from a transient Galactic ULX pulsar with L_x ≈ 5 × 10³⁹ erg s⁻¹ can be detected with kilometre-scale detectors such as IceCube if the source is within about 3–4 kpc. We also derived an upper limit on the neutrino flux from the Galactic ULX pulsar Swift J0243.6+6124 using IceCube data, a result that has not been previously reported. Our findings establish a new benchmark for future astrophysical neutrino observations, critical for interpreting data from current and upcoming instruments with significantly improved sensitivity.