A 682-second X-ray Periodicity in CH Cygni: Evidence for a Magnetic White Dwarf

Symbiotic stars are interacting binaries consisting of a red giant and typically a white dwarf, important as potential Type Ia supernova progenitors. Despite theoretical predictions that white dwarfs in symbiotic systems should often be magnetic, direct evidence has been elusive. We report the discovery of a $682.5 \pm 7$ s periodicity in the XMM-Newton X-ray light curve that we interpret as the spin period of the WD in CH Cygni. This detection provides strong evidence for a magnetic white dwarf in CH Cygni, making it only the second WD symbiotic star with confirmed X-ray pulsations after R Aquarii. Our discovery supports the magnetic propeller model previously proposed for CH Cygni's jet activity and state transitions.