Conclusion

The ASCA satellite observed the unusual X-ray pulsar GX 1+4 in September 1994. Assuming that two-photon cyclotron emission is the dominant emission mechanism in X-rays for this pulsar we have calculated the opening angle of the double-humped pulse predicted by the two-photon emission model, including the effects of gravitational light bending on the pulse shape. Light profiles of GX 1+4 exhibit opening angles of the shallow dip in the pulse consistent with the theoretically predicted maximum opening angle, although it is not certain that this phase represents the closest passage of the line-of-sight to the magnetic pole. The results are consistent with GX 1+4 having an unusually high surface magnetic field, or the wide opening angles may be evidence for the existence of more complicated emission region geometry than the simple slab model usually adopted. Analysis currently underway of XTE satellite high frequency observations, and more detailed analysis of pulse morphology, should help to give more information on the pulse morphology of GX 1+4.

© Copyright Astronomical Society of Australia 1997