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Relativistic jets are observed from accreting systems throughout the
Universe, and have a profound impact on their surroundings. Despite
their importance, the jet launching mechanism is not known. For accreting
neutron stars, the speed of their compact jets can reveal whether the
jets are powered by magnetic fields anchored in the accretion flow or
in the star itself. Russell et al. have observed the accreting neutron
star 4U 1728-34 with a simultaneous radio and X-ray observing
campaign. The radio observations, which probe the jet emission, were
taken over a 3-day period with the Australia Telescope Compact Array
(ATCA). X-ray monitoring, tracing the accretion flow and
detecting the thermonuclear explosions,
consisted of a single long observation with the International
Gamma-Ray Astrophysics Laboratory (INTEGRAL).
With these flares, they measured the speed of a neutron star compact
jet to be about one-third of the speed of light, much slower than
those from stellar mass black hole systems. This discovery provides a
powerful new tool for determining the role that individual
system properties have on the jet speed, revealing the dominant jet
launching mechanism.
The artist's impression above depicts how nuclear explosions on a neutron
star feed the jets being ejected from its magnetic polar
regions. (Image credit: Danielle Futselaar and Nathalie Degenaar,
Anton Pannekoek Institute, University of Amsterdam. License CC BY-SA
3.0)
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