Continuum Spectral Properties of Synchrotron Maser Emission: Comparison with Spontaneous Synchrotron Emission

Abstract

Abstract

Abstract Synchrotron maser emission (SME) is the continuum spectral manifestation of the electron cyclotron maser (ECM) instability in the relativistic regime, resulting from overlapping contributions of high-order cyclotron harmonics. In this work, we investigate the continuum spectral properties of SME and compare them with spontaneous synchrotron emission (SSE) under identical physical conditions. The SME spectrum is calculated by modeling the ECM instability from linear growth to quasi-linear saturation, while the SSE is calculated using the standard optically thin synchrotron radiation formalism. In both cases, the resulting intensities are treated as source-level quantities. The comparison shows that intensity, spectral morphology, and polarization have different diagnostic values. The source-level SME intensity is highly anisotropic and can be either higher or lower than the corresponding SSE intensity depending on the viewing direction. More robust distinctions are found in the spectral morphology: in the representative viewing directions considered here, SME produces narrower and more symmetric continuum spectra with systematically lower peak frequencies than SSE. The SME polarization is strongly angle dependent, with near-complete ordinary- and extraordinary-mode dominance along the favorable oblique and quasi-perpendicular directions, respectively, whereas SSE shows only weak ordinary-mode polarization. These results reveal distinct continuum spectral properties between SME and SSE, providing spectral diagnostics for identifying coherent emission mechanisms in broadband astrophysical radio sources.