A Multiwavelength Study of the 2025 Low State of the Intermediate Polar BG CMi

Abstract We present multiwavelength observations of the first recorded low state of the intermediate polar BG CMi. Optical monitoring of the source by members of the American Association of Variable Star Observers reveals a decrease of ∼0.5 mag that lasted ∼50 days in early 2025. During the low state the optical timing properties imply that BG CMi underwent a change in accretion mode, as power at the spin frequency ω dramatically dropped. An XMM-Newton observation revealed a substantial decrease in intrinsic absorption and a slight increase in intrinsic X-ray luminosity, compared to archival Suzaku data. Timing analysis of the X-ray light curves shows that power shifted from the orbital frequency Ω (prominent in Suzaku data) to 2Ω in the low-state XMM-Newton data, along with strengthening of certain orbital sidebands. We suggest that BG CMi transitioned to disk-overflow accretion, where the white dwarf accreted matter via both a disk and a stream, the latter becoming more dominant during the low state due to a decrease in the mass and size of the disk.