The outburst radial velocity curve of X-ray Nova Scorpii 1994 (= GRO J1655-40): a reduced mass for the black hole?

We present a re-analysis of the outburst radial velocity data for X-ray Nov a Scorpii 1994. Using a model based on X-ray heating of the secondary star, we suggest a more realistic treatment of the radial velocity data. Solutio ns are obtained in the (K-2,q) plane which, when combined with the publishe d value for the binary mass ratio and inclination, constrain the mass of th e black hole to within the region 4.1 < M-1 < 6.6 M-. (90 per cent confiden ce), which is significantly lower than the value obtained by Orosz & Bailyn , This reduced lower bound for the black hole mass, together with the high space velocity of the system, is consistent with the idea that it was forme d by the post-supernova collapse of a neutron star.