GRO J1655-40

This black hole binary was discovered in outburst by BATSE on July 27th, 1994. It showed great X-ray variability, and was found to be variable in the optical. It was observed at Woomera from August-October 1995.

Spectroscopic observations (from the literature) gave an orbital period of 2.62157 days. The Woomera data show definite variability over this time-scale, and also slight variability over tens of minutes.

VRI composite : a 12.6' x 9.8' field around GRO 1655-40 (it is shown by the tic marks). The low galactic latitude of this object is responsible for the large number of reddened stars in this image.

Diff. mag. vs. phase : all Woomera data phased at the orbital period. There is definite variability shown, but the form of the light-curve is complicated by the activity-state changes shown by this source.