Compact radio emission indicates a structured jet was produced by a binary neutron star merger

Area of Science:

• Astrophysics
• Multi-messenger Astronomy

Background:

• The binary neutron star merger GW170817 was observed via electromagnetic radiation and gravitational waves.
• The afterglow emission's origin (relativistic jet vs. isotropic outflow) remained uncertain.

Purpose of the Study:

• To differentiate between a narrow relativistic jet and an isotropic outflow for GW170817's afterglow.
• To determine the jet production rate in neutron star mergers.

Main Methods:

• Utilized very-long-baseline interferometry (VLBI) with 32 radio telescopes.
• Conducted observations 207.4 days post-merger.
• Measured the apparent source size and displacement.

Main Results:

• Constrained the apparent source size to be < 2.5 milli-arc seconds (90% confidence).
• Ruled out the isotropic outflow scenario due to the small observed size.
• Confirmed GW170817 produced a structured relativistic jet.

Conclusions:

• The observed afterglow is consistent with a structured relativistic jet.
• At least 10% of neutron star mergers are estimated to produce such jets.