Title: The nature of the hard X-ray component in Sco X-1
Proposal ID: 0120284
Subject category: Compact Object
Principal investigator: van der Klis
Institute: University of Amsterdam
Abstract
Scorpius X-1 is the archetypal neutron star binary; as the brightest X-ray binary and with an extremely
well-determined distance it offers a unique opportunity to quantitatively study the magnitude and spectrum
of accretion-powered emission processes. As well as thermal optical, UV and soft X-ray emission originating
in the viscous dissipation of gravitational potential energy, strongly non-thermal processes requiring a
large fraction of the accretion power budget are evident in radio and hard X-ray bands. Observations in
these two bands reveal the most energetic processes in such systems, diagnosing both the innermost accretion
flow, which is well within the strong-field gravity region near the neutron star and the relativistic
outflows (the radio jets). Recent work has revealed a strong link between these two relativistic regimes,
but the nature of this link is, as yet, unclear. Also in recent work, our most fundamental asumptions about
the energetics of the accretion/ejection processes have been called into question. We will use INTEGRAL,
together with ground-based facilities, to study these and related issues. By imaging the radio structure of
Scorpius X-1 (core-jet and 'lobe' impact sites) with intercontinental VLBI simultaneously with INTEGRAL
observations we can directly determine the relation between hard X-ray excess and jet in this system. By
combining INTEGRAL's wide band with optical/IR and radio we will obtain a unique coverage of the
electromagnetic as well as mechanical energy losses from the system.