Document Type


Publication Date


Publication Title

Monthly Notices of the Royal Astronomical Society


We present results of extensive CCD optical photometry (over 1000 frames representing ~150 hr of integration time) of the optical counterpart of the X-ray source GX339–4 obtained during the high (soft) state. The source was seen to be significantly variable. We do not, however, detect any periodic modulation with semi-amplitude greater than ~0.03 mag for periods less than ~0.5 day or semi-amplitude greater than ~0.07 mag for longer periods. An optical spectrum obtained shortly after GX339–4 made a transition from a ‘low’ to a ‘high’ state is also presented and compared with previous results. The width of the He IIλ4686 emission line in the spectrum implies that GX339–4 does not have an unusually low inclination angle and we therefore conclude that the orbital period of GX339–4 is probably longer than ~0.5 day.