Anisotropic x-ray transfer in a strongly magnetized plasma of the x-ray pulsar 4U 1626 - 67

The x-ray pulsar 4U 1626 - 67 was observed with Tenma during the period May 3 through 5, 1983. No appreciable change in the spectrum was observed during x-ray flares. The pulse period of 7.671350 s and the rate of period change are consistent with a stable spin-up at a rate of ∼ 2 x 10-4 yr-1. The pulse profile changes drastically at about 15 keV and 2 keV, and the energy spectrum depends on the pulse phase accordingly. No emission line feature of iron around 6 keV was found with an upper limit of the equivalent width of 60 eV (90 % confidence). The observed energy dependence of the x-ray pulse profile was simulated by a calculation based on the anisotropic radiation transfer in a strongly magnetized plasma with a magnetic field strength of ∼ 8 x 1012 G at the neutron star surface. (author)