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Abstract

Cataclysmic variable (CV) stars are interacting binary systems that exhibit exotic, multi-wavelength behavior driven by mass transfer from a donor star onto a white dwarf. As rich laboratories for accretion physics, binary dynamics, and the origins of Type Ia supernovae, CVs have been well studied in the X-ray, ultraviolet, optical, and infrared—but remain comparatively underexplored in the radio regime. This paper presents simultaneous, time-resolved optical and radio observations of the magnetic CV ST LMi, aimed at constraining its emission mechanisms and orbital modulation.
The optical light curves display brightness variations of approximately 1.31 ± 0.02 magnitudes on a period of 0.079089 days (approximately 114 minutes), consistent with the known orbital period. Fluxes are higher in longer-wavelength filters, consistent with cyclotron emission from a magnetically funneled accretion region. The radio data also exhibit strong orbital modulation (approximately 238.5 ± 27 μJy) but with a phase offset Δφ ≈ –0.40 relative to the optical peaks. This phase shift suggests that the radio emission originates from a region distinct from the optical accretion pole, likely near the L1 point and periodically eclipsed by the secondary. In addition, we observe variable circular polarization in the radio, ranging from weak levels (<5 >± 25% in quiescence) to 80 ± 17% during flux peaks.
Our findings strengthen the interpretation of electron cyclotron maser (ECM) as the dominant radio emission mechanism in magnetic CVs and provide new constraints on the spatial and temporal structure of radio-emitting regions in polars.

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