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Main Authors: Shaw, A. W., Mukai, K., Heinke, C. O., Nixon, C. G., Buckley, D. A. H., Dubovský, P. A., Hambsch, F. -J., Hilburn, J., Petrík, K., Plotkin, R. M., Potter, S. B., Rawat, N., Shahbaz, T., Dufoer, S., Dvorak, S., Messier, D., Myers, G., Nelson, P., Sabo, R., Ulowetz, J., Vanmunster, T.
Format: Preprint
Published: 2026
Subjects:
High Energy Astrophysical Phenomena
Online Access:https://arxiv.org/abs/2601.14156
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Table of Contents:
  • We present multi-wavelength 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 d in early 2025. During the low state the optical timing properties imply that BG CMi underwent a change in the 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 the 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.

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