Introduction

The variable X-ray source GX 1+4 associated with the M6III class giant V2116 Ophiuchi has exhibited a variety of interesting behaviour throughout the history of observations. The extended X-ray bright state of the 1970s, during which came the first detection (Lewin et al. 1971), was followed by a period of non-detection during the early 1980s and then a low intensity state which has persisted to this day. The pulse period is minutes. Average spin-up during the 1970's gave way to spin-down after the period of non-detection, although brief periods of spin-up have been detected recently (Chakrabarty et al. 1997). The measured rates of spin-up and spin-down ( per annum) are similar in magnitude and are among the fastest known for any pulsar.

A large set of pulse profiles taken at different times and in different intensity states now exists. Because of their strong energy dependence and great variability, relative phasing between observations at different times and energies is not clear. In this paper we report the results of a study of these published profiles using the wide energy range observations of White et al. (1983) to determine their relative phases. We show evidence of an association between X-ray luminosity (), the spin-up/spin-down state and the pulse shape.

© Copyright Astronomical Society of Australia 1997