Opening
The 2015 detection of gravitational waves from merging black holes marked a watershed moment in astronomy, but it was the 2017 observation of GW170817—a binary neutron star merger detected simultaneously in gravitational waves and across the electromagnetic spectrum—that truly inaugurated the multimessenger era. Now, as the LIGO, Virgo, and KAGRA interferometers prepare for their fifth observing run and next-generation detectors loom on the horizon, a new question emerges: how can we best catch and characterize the electromagnetic counterparts to these cosmic collisions? A new paper by Colombo, Giroletti, Vergani, and colleagues argues that radio observations—particularly those enabled by the Square Kilometre Array Observatory (SKAO)—will be essential to answering this question.
What they found
The authors present a comprehensive overview of how radio observations can constrain the properties of gamma-ray bursts (GRBs) and kilonovae produced by gravitational wave events. Their key insight is that radio emission from GRB afterglows remains detectable for very long timescales, making radio observations uniquely suited for identifying and tracking merger counterparts long after optical and X-ray signals fade. This extended visibility window enables precise characterization of system evolution and detailed probing of GRB jet structures.
Notably, the authors highlight that radio observations may enable possible detection of misaligned jets once their velocity becomes non-relativistic—a regime where jets initially beamed away from Earth could become visible as they decelerate. This capability has already been demonstrated: connected interferometers and VLBI arrays proved essential in constraining the ejecta properties of GW170817, the benchmark event for multimessenger astronomy.
!Illustration of radio emission timescales from GRB afterglows and merger counterparts
The authors argue that even SKAO in its initial configuration (AA) will provide the sensitivity and field of view needed to complement GW counterpart searches during the upcoming O5 observing run and beyond. Beyond individual event follow-up, they emphasize that SKAO will enable population studies of the properties of both long GRBs (produced by massive star collapse) and short GRBs (produced by neutron star mergers)*, along with their jets and environments.
Why it matters
Radio observations occupy a unique niche in multimessenger astronomy. While gravitational wave detectors pinpoint merger locations and optical surveys hunt for kilonovae, radio telescopes provide long-term monitoring that constrains the physical properties of relativistic jets and merger ejecta. This complementary approach is essential for understanding the connection between gravitational wave sources and their electromagnetic signatures—a connection that remains incompletely characterized despite GW170817.
What's next
The authors frame their work as a roadmap for the coming decade. As next-generation detectors like the Einstein Telescope, Cosmic Explorer, and LISA come online in the 2030s, the demands on electromagnetic follow-up will intensify. SKAO's capabilities will be tested during O5, offering a preview of how radio observations can enhance multimessenger science in the era of frequent GW detections.
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