Astrophysicists Shocked by Short Gamma Ray Burst Afterglow 10 Billion Light Years Away

Rare occasion happened 10 billion lightyears away, 3.8 billion years after the Big Bang

• SGRB181123B is the most remote brief gamma ray burst with its afterglow determined
• Incredibly quickly and faint, these occasions are infamously challenging to capture
• Event provides an uncommon chance to study these systems in a much more youthful universe
• New research study reveals that neutron stars in a ‘teenage’ universe might combine reasonably rapidly

The further away an item depends on deep space, the fainter it appears through the lens of a telescope.

So when a Northwestern University-led group of astrophysicists spotted an afterglow of a brief gamma ray burst (SGRB) situated 10 billion light years away, they were surprised. Afterglows, after all, are currently extremely faint and quick signals — in some cases long lasting simple hours.

Known as SGRB181123B, the burst happened simply 3.8 billion years after the Big Bang. It is the 2nd most-distant reputable SGRB ever spotted and the most remote occasion with an optical afterglow.

“We certainly did not expect to discover a distant SGRB, as they are extremely rare and very faint,” stated Northwestern’s Wen-fai Fong, a senior author of the research study. “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.”

“We believe we are uncovering the tip of the iceberg in terms of distant SGRBs,” stated Kerry Paterson, the research study’s very first author. “That motivates us to further study past events and intensely examine future ones.”

The research study was released on July 14, 2020, in the Astrophysical Journal Letters.

Short gamma ray bursts throughout deep space. An artist’s impression of how SGRB11823B compares to other brief gamma ray bursts. Except when they are spotted by gravitational wave observatories, the gamma ray bursts can just be spotted from Earth when their jets of energy are pointed towards us. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. Pollard/K. Paterson & W. Fong (Northwestern University). Image processing: Travis Rector (University of Alaska Anchorage), Mahdi Zamani & Davide de Martin

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

Some of the most energetic and brightest surges in deep space, SGRBs more than likely happen when 2 neutron stars combine. This merger triggers a temporary burst of gamma rays, which is the most energetic type of light. Astronomers generally just discover 7 or 8 SGRBs each year that are well-localized enough for more observations. And due to the fact that their afterglows generally last, at the majority of, a couple of hours prior to fading into oblivion, they seldom remain enough time for astronomers to get a close appearance.

But with SGRB181123B, astronomers got fortunate. NASA’s Neil Gehrels Swift Observatory initially spotted the occasion on Thanksgiving night in 2018. Within hours, the Northwestern group from another location accessed the global Gemini Observatory, utilizing the Gemini-North telescope, situated atop Mauna Kea in Hawaii. Using this 8.1-meter telescope, the scientists determined SGRB181123B’s optical afterglow. 

With follow-up observations utilizing Gemini-South in Chile, MMT in Arizona and Keck in Hawaii, the group understood SGRB181123B might be more remote than the majority of.

“We were able to obtain deep observations of the burst mere hours after its discovery,” Paterson stated. “The Gemini images were very sharp, allowing us to pinpoint the location to a specific galaxy in the universe.”

“With SGRBs, you won’t detect anything if you get to the sky too late,” Fong included. “But every once in a while, if you react quickly enough, you will land on a really beautiful detection like this.” 

A peek into ‘cosmic high noon’

To reveal the SGRB’s range from Earth, the group then accessed a near-infrared spectrograph on Gemini-South, which can penetrate redder wavelengths. By taking a spectrum of the host galaxy, the scientists understood they had actually serendipitously discovered a far-off SGRB.

After determining the host galaxy and determining the range, Fong, Paterson and their group had the ability to identify essential homes of the moms and dad excellent populations within the galaxy that produced the occasion. Because SGRB181123B appeared when deep space was just about 30% of its existing age — throughout a date called “cosmic high noon” — it provided an uncommon chance to study the neutron star mergers from when deep space was a “teenager.”

When SGRB181123B happened, deep space was extremely hectic, with quickly forming stars and fast-growing galaxies. Massive binary stars require time to be born, progress and pass away — lastly becoming a set of neutron stars that ultimately combine.

“It’s long been unknown how long neutron stars — in particular those that produce SGRBs — take to merge,” Fong stated. “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.”

Reference: “Discovery of the optical afterglow and host galaxy of short GRB181123B at z=1.754: Implications for Delay Time Distributions” by K. Paterson, W. Fong, A. Nugent, A. Rouco Escorial, J. Leja, T. Laskar, R. Chornock, A. A. Miller, J. Scharwächter, S. B. Cenko, D. Perley, N. R. Tanvir, A. Levan, A. Cucchiara, B. E. Cobb, K. De, E. Berger, G. Terreran, K. D. Alexander, M. Nicholl, P. K. Blanchard, D. Cornish, Astrophysical Journal Letters.
arXiv: 2007.03715

The research study, “Discovery of the optical afterglow of short GRB 181123B at z = 1.754: Implications for delay time distributions,” was supported by the National Science Foundation (NSF) (award numbers AST-1814782 and AST-1909358) and NASA (award number HST-GO-15606.001-A). For this work, scientists utilized the International Gemini Observatory, Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory and the Community Science and Data Center — which are all Programs of NSF’s NOIRLab — in addition to MMT Observatory, W.M. Keck Observatory and the Vera C. Rubin Observatory.