Two Years of Observations of the X-ray Pulsar SMC X-1 with the ART-P   Telescope onboard the Granat Observatory
  We present the observations of the pulsar SMC X-1 with the ART-P telescope onboard the Granat observatory. We investigate the variability of the flux from the source on time scales of several tens of days. The intensity variation of the pulsar are shown to be consistent with the presence of a periodicity in the system with a characteristic time scale of $\sim61$ days. The precession of an inclined accretion disk, as indirectly confirmed by the absence of low-state pulsations, may be responsible for the observed variability. The spectrum of the source is well described by a power-law energy dependence of the photon flux density with a slope of $\sim1.5$ and an exponential cutoff at energies above $\sim14-18$ keV. We estimated the inclinations between the planes of the orbit and the accretion disk and the magnetic field of the neutron star. 
A.A.Lutovinov (1,2), S.S.Tsygankov (1), S.A.Grebenev (1),   M.N.Pavlinsky (1), R.A.Sunyaev (1,2) (1 - Space Research Institu...