| 25th of February 2019 |
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| VLBI observations of GW 170817 afterglow |
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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–arc 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.) |