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25th of February 2019
VLBI observations of GW 170817 afterglow
Ghirlanda et al. last week published in Science the results of Very Long Baseline Interferometry (VLBI) observations of the afterglow of the binary neutron star merger event GW170817. The afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow, and only high angular-resolution measurements of the source size and displacement enabled by VLBI could discriminate between these scenarios. A global network of 32 radio telescopes, including elements of the southern hemisphere Long Baseline Array, constrained the source size to be smaller than 2.5 milli‚Äďarc seconds. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Observations were performed at a central frequency of 4.85 GHz with a total bandwidth of 256 MHz.

The image shows an artist's impression of the outcome of the GW 170817 neutron star merger, with the ultra-fast jet moving at nearly the speed of light, indicating it has broken through the shell of expelled matter unhindered. (Image credit: Beabudai Design and Forbes.)

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