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We report XMM-Newton and TESS observations of V496 UMa, an AM Herculis-typecataclysmic variable. The XMM-Newton observation reveals that at times, twopoles on the white dwarf accrete simultaneously, but accretion onto thesecondary magnetic pole is erratic and can nearly cease in less than one binaryorbit (1.5 h). Modelling of the X-ray spectrum during the primary maximumreveals no change in the accretion structures onto the primary pole whenaccretion onto the secondary pole is disrupted, suggesting that the disruptionof accretion onto the secondary pole may be caused by mass-transfer variationsfrom the donor star. The TESS observation, which spanned eight weeks at atwo-minute cadence, shows a stable, double-humped orbital modulation due tocyclotron emission from the post-shock region, while the observed times ofmaximum light show a slow systematic drift that does not correlate with thesystem's overall brightness.

Transient two pole accretion in the polar V496 UMa