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Relaxation of time-variable neutron-loaded relativistic jets across the photosphere and their GeV-TeV neutrino counterparts

Kanako Nakama1,*, Kazumi Kashiyama1, and Nobuhiro Shimizu2

  • *Contact author: kanako.nakama@astr.tohoku.ac.jp
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Phys. Rev. D 113, 103036 – Published 26 May, 2026

DOI: https://doi.org/10.1103/4ryg-bzc7

Abstract

Both observational and theoretical studies indicate that the central engine of a gamma-ray burst (GRB) is intrinsically time-variable, implying jet inhomogeneity. A jet with an inhomogeneous Lorentz factor distribution develops internal shocks both below and above the photosphere, relaxing toward homologous expansion. Below the photosphere, neutrons, whose mean free paths are much longer than those of charged particles, play an essential role in the dissipation process. Using neutron-inclusive shell simulations with initial conditions based on the collapsar scenario, we link the statistical inhomogeneity of the jet at the breakout of the progenitor to the dissipation that occurs inside and outside the photosphere, and calculate the GeV-TeV neutrino counterpart originated from inelastic neutron-proton interactions consistently with the prompt gamma-ray emission. We find that the peak energy of the GeV-TeV neutrinos is in 10–30 GeV irrespective of the baryon loading factor of the jet, with the high-energy tail extending into the TeV range as the amplitude of the time variability becomes stronger. When gamma-ray emission is efficient as in typical GRBs (i.e., the bolometric gamma-ray radiation efficiency with respect to the total engine-injected jet power is ≲100%), the radiative efficiency of GeV-TeV neutrinos remains 0.1%–10%. By contrast, when the gamma-ray radiation efficiency is relatively low (≲10%) for jets where a large fraction of the energy is dissipated below the photosphere, the neutrino efficiency can increase up to 20%. This suggests that GRBs with relatively low gamma-ray luminosities, as well as x-ray-rich transients, can be promising targets for ongoing and future GeV-TeV neutrino transient searches.

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Phys. Rev. D 113, 103036– Published 26 May, 2026
  • Received 21 December 2025
  • Accepted 10 March 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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