Kepler K2 Measurement of the Rotational Period of the Intermediate Polar 1RXS J180431.1-273932

1RXS J180431.1-273932 is an intermediate polar: a cataclysmic variable star with a rapidly rotating, magnetized white dwarf. We analyze the system’s Kepler K2 short-cadence light curve and identify a strong, highly coherent pulse with a period of 0.0057171 ± 0.0000002 days, which matches the proposed white dwarf rotational period identified in previous X-ray studies. We establish an ephemeris for the optical spin pulse.