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Photon Propagation through Magnetar-Hosted Axion Clouds: Time Delays and Polarimetric Constraint

M. M. Chaichian, B. A. Couto e Silva, B. L. Sánchez-Vega

Abstract

Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos provide a useful probe of propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to magnetars. Working within the Euler-Heisenberg effective theory extended by the axion sector, we derive the modified photon dispersion relations in the presence of a strong magnetic background and an oscillating axion field. We show that axion-photon mixing turns the magnetized vacuum into an anisotropic birefringent medium, leading to geometry-dependent deviations from luminal propagation and kinematic time delays that reach $Δt_{\perp}\simeq1.33\times10^{-12}\,\mathrm{s}$ for orthogonal propagation. Although this effect is many orders of magnitude larger than the delays expected in diffuse astrophysical backgrounds, it remains far too small to account for the macroscopic offsets discussed in current multimessenger candidates. We further show that the same birefringent medium constrains the survival of the intrinsic linear polarization of prompt GRB emission, yielding the environmental bound $g_{aγγ}\lesssim6.02\times10^{-14}\,\mathrm{GeV}^{-1}$ for benchmark magnetar-scale parameters and axion masses near $m_a\sim10^{-4}\,\mathrm{eV}$. Magnetar-hosted axion clouds thus emerge as complementary environments in which dispersive transport and polarimetric observables jointly probe axion electrodynamics.

Photon Propagation through Magnetar-Hosted Axion Clouds: Time Delays and Polarimetric Constraint

Abstract

Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos provide a useful probe of propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to magnetars. Working within the Euler-Heisenberg effective theory extended by the axion sector, we derive the modified photon dispersion relations in the presence of a strong magnetic background and an oscillating axion field. We show that axion-photon mixing turns the magnetized vacuum into an anisotropic birefringent medium, leading to geometry-dependent deviations from luminal propagation and kinematic time delays that reach for orthogonal propagation. Although this effect is many orders of magnitude larger than the delays expected in diffuse astrophysical backgrounds, it remains far too small to account for the macroscopic offsets discussed in current multimessenger candidates. We further show that the same birefringent medium constrains the survival of the intrinsic linear polarization of prompt GRB emission, yielding the environmental bound for benchmark magnetar-scale parameters and axion masses near . Magnetar-hosted axion clouds thus emerge as complementary environments in which dispersive transport and polarimetric observables jointly probe axion electrodynamics.

Paper Structure

This paper contains 16 sections, 88 equations, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. Theoretical Framework
  3. Theoretical Setup and Field Equations
  4. Dispersion Relations and Canonical Propagation Modes
  5. Longitudinal mode
  6. Transverse mode
  7. Calculating the Time Delay
  8. Polarization Survival and Exclusion Bounds
  9. Conclusions
  10. Numerical Determination of the Dispersion Root
  11. Precision and stability.
  12. Root identification and physical filters.
  13. Group-velocity extraction.
  14. Validation.
  15. Estimate of Magnetar Encounter Probability
  16. ...and 1 more sections

Figures (1)

  • Figure 1: Axion-photon coupling as a function of the axion mass, obtained in Ref. AxionLimits. The shaded regions indicate existing constraints from astrophysical observations and laboratory searches, while projected sensitivities of future experiments are also shown. The dark shaded region represents the polarization-survival benchmark bound derived in this work over the mass range $10^{-9} \lesssim m_a \lesssim 10^{-4}\,\mathrm{eV}$ relevant for magnetar-hosted axion clouds, for the benchmark values of $D_{\rm int}$, $B_T$, and $\Delta\omega$ adopted in the text.