OPTICAM reveals hints of cyclotron emission from the intermediate polar V709 Cas

Abstract

Magnetic cataclysmic variables of the intermediate polar (IP) subclass display a wide range of variability across different wavelengths. In late 2024 October/early November, the IP V709 Cas was observed over 10 nights by the OPtical TIming CAMera at the San Pedro Mártir Observatory in simultaneous three-colour (g, r, and i, or z band) photometry. On two of these nights, V709 Cas was simultaneously observed by the Neutron star Interior Composition ExploreR X-ray telescope. A periodogram analysis of the optical g- and r-band light curves reveals no prominent features at the white dwarf (WD) spin, but prominent features at the spin-orbit beat. In contrast, the X-ray and near-infrared (near-IR) i- and z-band periodograms show prominent features at the spin, but not the spin-orbit beat. Optical beat and near-IR spin pulsations have been seen in the IP PQ Gem, with simultaneous circular polarization detected in the near-IR, indicating cyclotron origin. We therefore speculate that we are seeing cyclotron radiation from V709 Cas, possibly adding it to the small group of cyclotron-emitting IPs. Combining analytical approximations with our expectation for cyclotron harmonics in the near-IR, we suggest a WD magnetic field strength of 10 MG < B < 40 MG.

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ORCID for D. Altamirano: orcid.org/0000-0002-3422-0074

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