Fast work captures fleeting SGRB

Astronomers have confirmed the discovery of the second-most distant well-established short gamma-ray burst (SGRB) ever detected and the most distant with an optical afterglow.

Observations from a suite of the world’s biggest telescopes place the event at 10 billion light-years away, they say, squarely in the epoch of cosmic high noon when the Universe was in its “teenage years” and rapidly forming stars.

The appearance of an SGRB at such an early time could alter theories about their origins, particularly the length of time it takes two neutron stars to merge and produce these powerful explosions, as well as the rate of neutron star mergers in the young Universe.

“This was a very exciting object to study,” says lead researcher Kerry Paterson from Northwestern University, US. “Our research now suggests neutron star mergers could occur surprisingly quickly for some systems, with neutron star binaries spiralling together in less than a billion years to create an SGRB.”

The discovery is described in paper accepted for publication in The Astrophysical Journal Letters and currently available on the preprint server arXiv.

SGRBs are short-lived, highly-energetic bursts of gamma-ray light. The light lasts for less than two seconds, and the optical light just a matter of hours before fading, so speed is of the essence in following up the optical afterglow.

NASA’s Neil Gehrels Swift Observatory sent out a worldwide alert after first detecting the event, now known as SGRB181123B, and within hours the Northwestern team had remotely accessed the international Gemini Observatory, using the Gemini-North telescope in Hawaii.

When follow-up observations were made using Gemini-South in Chile, the MMT Observatory in Arizona and the WM Keck Observatory in Hawaii, Paterson and colleagues realised SGRB181123B was likely more distant than most.

“The Gemini images were very sharp, allowing us to pinpoint the location to a specific galaxy in the Universe,” she says.

To uncover the SGRB’s distance from Earth, the team accessed a near-infrared spectrograph on Gemini-South, which can probe redder wavelengths. They were then able to determine key properties of the parent stellar populations within the galaxy that produced the event.

Because SGRB181123B appeared when the Universe was only about 30% of its current age, it offered a rare opportunity to study the neutron star mergers at a time when things were incredibly busy, with rapidly forming stars and fast-growing galaxies.