GX 1+4 : pulse period measurement and detection of phase-variable iron line emission.

Observations of the X-ray source GX 1+4 (1728 - 247) made by Ariel 6 in 1979 July and 1980 April show that the pulse period decreased at a faster rate during 1978-80 than over the period 1970-78. Compared with that measured in 1976, the pulse profile had become more sinusoidal, with an apparent phase lag of 0.1 between the 4-8 keV pulse and that seen at energies above 25 keV. The 1-4 keV range does not show pulsations and is stronger than hitherto. There is also an iron emission feature whose equivalent width varies with pulse phase.