Short gamma-ray bursts (SGRBs) are powerful explosions that last less than two seconds and are likely produced in the merger between a neutron star and another compact object. These events release a huge amount of gamma-rays but they can also leave an afterglow in visible light. Researchers have now spotted the most distant one yet.
Emissions from SGRB181123B, as it is known, come from 10 billion light-years away. As reported in The Astrophysical Journal Letters, this is the second-furthest GRB ever detected but the furthest with an optical afterglow. This rare feature was crucial in expanding our understanding of this rare phenomenon.
“We certainly did not expect to discover a distant SGRB, as they are extremely rare and very faint,” senior author Wen-fai Fong, from Northwestern University, said in a statement. “We perform ‘forensics’ with telescopes to understand its local environment, because what its home galaxy looks like can tell us a lot about the underlying physics of these systems.”
Every year, there are only seven or eight SGRBs. Optical afterglows last for only a few hours, which means follow-up observations need to occur with a rapid turnaround time to catch them. The rarity of the event combined with its distance makes it a crucial contribution to the field.
“We believe we are uncovering the tip of the iceberg in terms of distant SGRBs,” explained Kerry Paterson, the study’s first author also at Northwestern. “That motivates us to further study past events and intensely examine future ones.”
The optical observation allowed researchers to establish its distance and the parent population that produced the SGRB. The stars must have had time to evolve into neutron stars, and those neutron stars needed time to merge. This event is an important window into what the universe was like 3.8 billion years after the Big Bang.
“It’s long been unknown how long neutron stars — in particular those that produce SGRBs — take to merge,” Fong said. “Finding an SGRB at this point in the universe’s history suggests that, at a time when the universe was forming lots of stars, the neutron star pair may have merged fairly rapidly.”
The SGRB was detected by NASA’s Swift gamma-ray observatory and was followed up by several optical telescopes in Hawaii, Chile, and Arizona.