Variations of the pulse profile and the X-ray intensity of GX301-2 (4U1223-62)

Two successive X-ray outbursts of the recurrent X-ray pulsar GX301-2 were observed in April and May, 1982 from Hakucho. Apart from general increase during flares lasting for several days, the X-ray intensity was highly variable on a time-scale of the order of an hour. The outstanding feature is that the amplitude of 700 s pulsation of GX301-2 changes rapidly in a very wide range. When the pulsation is distinct, the depth of modulation is as large as 60%; whereas, the pulse amplitude occasionally diminishes almost to an undetectable level so that the observed X-rays become unpulsed. Such drastic changes are found to occur at any intensity levels observed. In several cases of abrupt changes of pulse amplitude, the intensity at the pulse bottom remained essentially unchanged. These properties suggest a hypothesis that the X-ray emission from GX301-2 consists of a pulsating component with variable amplitude and a non-pulsating component of less variable intensity.