title: An ultra-relativistic outflow from a neutron star accreting gas from a companion.
abstract: Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon.
authors.affiliation: Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands. rpf@science.uva.nl
authors.forename: Rob
authors.initials: R
authors.lastname: Fender
authors.forename: Kinwah
authors.initials: K
authors.lastname: Wu
authors.forename: Helen
authors.initials: H
authors.lastname: Johnston
authors.forename: Tasso
authors.initials: T
authors.lastname: Tzioumis
authors.forename: Peter
authors.initials: P
authors.lastname: Jonker
authors.forename: Ralph
authors.initials: R
authors.lastname: Spencer
authors.forename: Michiel
authors.initials: M
authors.lastname: Van Der Klis