Spectral and Polarization Properties of Coherent Radio Emission from Relativistic Magnetized Pair Plasma Shocks
Abstract
Fast radio bursts (FRBs) are millisecond-duration radio transients whose emission mechanism remains an open question. The so-called synchrotron maser instability in relativistic magnetized shocks is a leading candidate for FRBs produced outside the compact object magnetosphere, yet its spectral and polarization predictions have not been systematically explored. We present three-dimensional particle-in-cell simulations of relativistic magnetized pair plasma shocks with upstream magnetization σ> 1 and bulk Lorentz factor γ0 = 10, assuming a plane-parallel shock geometry and neglecting radiative cooling, and compute the spectra and polarization of the precursor maser emission for an arbitrary line of sight. For on-axis observers aligned with the shock-propagation direction, the X-mode dominates the emission. The O-mode power increases at off-axis viewing angles and is primarily associated with currents parallel to the upstream background magnetic field. Assuming a spherical shock, we find full-width-at-half-maximum fractional bandwidths of Δν/ν0≃0.57 and $0.82$ for σ=3 and $6$, respectively. For highly magnetized shocks, the intrinsic emission bandwidth accounts for most of the spectral width, while high-latitude contributions provide additional broadening. The integrated emission remains highly linearly polarized near the spectral peak, with a nearly constant polarization angle due to the dominance of the X-mode. Our results suggest that synchrotron maser emission can produce spectra with bandwidths and high linear polarization degrees compatible with observations of some non-repeating FRBs, and may provide testable signatures for distinguishing shock-powered FRBs from other emission mechanisms.
Related
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BibTeX
@misc{qu2026spectral,
title = {{Spectral and Polarization Properties of Coherent Radio Emission from Relativistic Magnetized Pair Plasma Shocks}},
author = {Yuanhong Qu and Joonas Nättilä and Lorenzo Sironi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30494},
eprint = {2609.30494},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30494},
}
RIS
TY - UNPB
TI - Spectral and Polarization Properties of Coherent Radio Emission from Relativistic Magnetized Pair Plasma Shocks
AU - Yuanhong Qu
AU - Joonas Nättilä
AU - Lorenzo Sironi
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.30494
UR - https://arxiv.org/abs/2609.30494
AB - Fast radio bursts (FRBs) are millisecond-duration radio transients whose emission mechanism remains an open question. The so-called synchrotron maser instability in relativistic magnetized shocks is a leading candidate for FRBs produced outside the compact object magnetosphere, yet its spectral and polarization predictions have not been systematically explored. We present three-dimensional particle-in-cell simulations of relativistic magnetized pair plasma shocks with upstream magnetization σ> 1 and bulk Lorentz factor γ_0 = 10, assuming a plane-parallel shock geometry and neglecting radiative cooling, and compute the spectra and polarization of the precursor maser emission for an arbitrary line of sight. For on-axis observers aligned with the shock-propagation direction, the X-mode dominates the emission. The O-mode power increases at off-axis viewing angles and is primarily associated with currents parallel to the upstream background magnetic field. Assuming a spherical shock, we find full-width-at-half-maximum fractional bandwidths of Δν/ν_0≃0.57 and $0.82$ for σ=3 and $6$, respectively. For highly magnetized shocks, the intrinsic emission bandwidth accounts for most of the spectral width, while high-latitude contributions provide additional broadening. The integrated emission remains highly linearly polarized near the spectral peak, with a nearly constant polarization angle due to the dominance of the X-mode. Our results suggest that synchrotron maser emission can produce spectra with bandwidths and high linear polarization degrees compatible with observations of some non-repeating FRBs, and may provide testable signatures for distinguishing shock-powered FRBs from other emission mechanisms.
ER -