The brief gamma-ray burst leaves the most distant optical glow detected

The farther an object is in the universe, the fainter it is seen through the lens of a telescope.

So when a team of astrophysicists led by Northwestern University detected a short gamma-ray burst (SGRB) glow located 10 billion light-years away, they were shocked. Subsequent blazes, after all, are already incredibly weak and fast signals, sometimes lasting only a few hours.

Known as SGRB181123B, the explosion occurred just 3.8 billion years after the Big Bang. It is the second most distant well-established SGRB ever detected and the most distant event with a subsequent optic glare.

“We certainly did not expect to discover a distant SGRB, as they are extremely rare and very weak,” said Wen-fai Fong of Northwestern, lead author of the study. “We do ‘forensic analysis’ with telescopes to understand their local environment, because the appearance of their galaxy can tell us a lot about the underlying physics of these systems.”

Kerry Paterson, the study’s first author, said: “We believe we are discovering the tip of the iceberg in terms of distant SGRBs. That motivates us to continue studying past events and intensely examining future ones.”

The study will be published in Astrophysical charts.

Fong is an assistant professor of physics and astronomy at Northwestern Weinberg College of Arts and Sciences and a member of CIERA (Center for Interdisciplinary Research and Exploration in Astrophysics). Paterson is a postdoctoral associate at CIERA.

Some of the brightest and most energetic explosions in the universe, SGRBs probably occur when two neutron stars merge. This fusion causes a short-lived gamma-ray burst, which is the most energetic form of light. Astronomers typically only detect seven or eight SGRBs each year that are well enough localized for additional observations. And because their glows typically last at most a few hours before fading into oblivion, they rarely linger long enough for astronomers to get a close look.

But with SGRB181123B, astronomers were lucky. NASA’s Neil Gehrels Swift Observatory first detected the event on Thanksgiving night in 2018. Within hours, the Northwest team remotely accessed the International Gemini Observatory, using the Gemini-North telescope, located on top of Mauna Kea in Hawaii. Using this 8.1-meter telescope, the researchers measured the optical glare of the SGRB181123B.

With follow-up observations using Gemini-South in Chile, MMT in Arizona, and Keck in Hawaii, the team realized that SGRB181123B may be more distant than most.

“We were able to obtain deep observations of the explosion a few hours after its discovery,” Paterson said. “The Gemini images were very sharp, allowing us to determine the location of a specific galaxy in the universe.”

Fong added, “With SGRBs, it won’t detect anything if it reaches the sky too late. But every now and then, if you react fast enough, you will come across really beautiful detection like this.”

A look at a cosmic noon

To discover the distance of the SGRB from Earth, the team accessed a near-infrared spectrograph at Gemini-South, which can probe redder wavelengths. By taking a spectrum from the host galaxy, the researchers realized that they had accidentally discovered a distant SGRB.

After identifying the host galaxy and calculating distance, Fong, Paterson, and their team were able to determine the key properties of the main stellar populations within the galaxy that produced the event. Because SGRB181123B appeared when the universe was only 30% of its current age, during a time known as “cosmic high noon,” it offered a rare opportunity to study neutron star mergers from when the universe was a “teenager.” .

When SGRB181123B occurred, the universe was incredibly busy, with rapidly forming stars and fast-growing galaxies. Massive binary stars take time to birth, evolve, and die, eventually becoming a pair of neutron stars that eventually merge.

“It has long been unknown how long it takes for neutron stars, particularly those producing SGRB, to fuse,” Fong said. “Finding an SGRB at this point in the history of the universe suggests that, at a time when the universe was forming a lot of stars, the pair of neutron stars may have merged quite quickly.”