The origin of Scorpius X-1

Abstract

We have used multi-wavelength observations of high precision to derive the space velocity and compute the orbit around the Galactic Centre of the prototype X-ray binary Scorpius X-1. An origin in the local spiral arm of the Milky Way is ruled out. The galactocentric kinematics of Scorpius X-1 is similar to that of the most ancient stars and globular clusters of the inner Galactic halo. Most probably, this low-mass X-ray binary was formed by a close encounter in a globular cluster. However, it cannot be ruled out that a natal supernova explosion launched Scorpius X-1 into an orbit like this from a birth place in the galactic bulge. In any case, the Galactocentric orbit indicates that Scorpius X-1 was formed more than 30 Myrs ago.