The 16 days periodicity observed in the Fast Radio Burst ( FRB ) source FRB 180916.J0158+65 by the CHIME telescope is consistent with that of a tight , stellar mass binary system of semi-major axis \sim \mbox { few } \times 10 ^ { 12 } cm . The primary is an early OB-type star with mass loss rate \dot { M } \sim 10 ^ { -8 } -10 ^ { -7 } M _ { \odot } yr ^ { -1 } and the secondary a neutron star . The observed periodicity is not intrinsic to the FRB ’ s source , but is due to the orbital phase-dependent modulation of the absorption conditions in the massive star ’ s wind . The observed relatively narrow FRB activity window implies that the primary ’ s wind dynamically dominates that of the pulsar , \eta = L _ { sd } / ( \dot { M } v _ { w } c ) \leq 1 , where L _ { sd } is pulsar spin-down , \dot { M } is the primary ’ s wind mass loss rate and v _ { w } is its velocity . The condition \eta \leq 1 requires mildly powerful pulsar with L _ { sd } \lesssim 10 ^ { 37 } erg s ^ { -1 } . The observations are consistent with magnetically-powered radio emission originating in the magnetospheres of strongly magnetized neutron stars , the classical magnetars .