2000ApJ...542L..41K

Modulations detected in the observed spin period of the 34 ms X-ray pulsar SAX J0635+0533 show that the pulsar is in a binary system with a period of 11.2±0.5 days, a projected orbital semimajor axis asini=83±11 lt-s, a mass function in the range of 3.4-7.8 M_☉, and an orbital eccentricity of 0.29±0.09. A combination of observations spanning 2 yr places a lower bound on the intrinsic period derivative of the pulsar of 3.8x10^–13. The period derivative implies a high torque on the neutron star that would require a very high mass accretion rate, in excess of 6x10^–7 M_☉.yr^–1, if produced via accretion. The torque and X-ray luminosity are both within the range typical of young, rotation-powered pulsars.