Astronomers trace short bursts of gamma rays farther into the distant universe

Using several highly sensitive instruments and sophisticated galaxy modeling, the researchers identified the galactic foci of 84 SGRBs and probed the characteristics of 69 of the identified host galaxies. Credit: Image by WM Keck Observatory/Adam Makarenko

The most robust inventory to date lists host galaxies and characteristics of SGRBs.

• Using observations and modeling, astronomers have identified the origins of 84 SGRBs, quadrupling the existing samples.
• They found that 85% of SGRBs in the catalog came from young galaxies in active star formation, and 20-40% of SGRBs occurred when the universe was much younger.
• The team also discovered that several SGRBs were spotted outside their host galaxies, as if they had been “expelled”.
• Researcher: “Our catalog will serve as a reference for comparison with future detections of
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A team of astronomers, led by

Using several highly sensitive instruments and sophisticated galaxy modeling, the scientists pinpointed the galactic homes of 84 SGRBs and probed the characteristics of 69 of the identified host galaxies. Among their findings, they discovered that about 85% of the studied SGRBs come from young, actively star-forming galaxies.

The astronomers also found that more SGRBs occurred at earlier times, when the universe was much younger — and with greater distances from their host galaxies’ centers — than previously known. Surprisingly, several SGRBs were spotted far outside their host galaxies — as if they were “kicked out,” a finding that raises questions as to how they were able to travel so far away.

“This is the largest catalog of SGRB host galaxies to ever exist, so we expect it to be the gold standard for many years to come,” said Anya Nugent, a Northwestern graduate student who led the study focused on modeling host galaxies. “Building this catalog and finally having enough host galaxies to see patterns and draw significant conclusions is exactly what the field needed to push our understanding of these fantastic events and what happens to stars after they die.”

Short gamma-ray burst host galaxies across cosmic time. Credit: W.M. Keck Observatory/Adam Makarenko

The team published two papers, detailing the new catalog. Both papers were published in The Astrophysical Journal on Monday, November 21. Because SGRBs are among the brightest explosions in the universe, the team calls its catalog BRIGHT (Broadband Repository for Investigating Gamma-ray burst Host Traits). All of BRIGHT’s data and modeling products are publicly available online for community use.

Nugent is a graduate student in physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). She is advised by Wen-fai Fong, an assistant professor of physics and astronomy at Weinberg and a key member of CIERA, who led a second study focused on SGRB host observations.

Benchmark for future comparisons

When two neutron stars collide, they generate momentary flashes of intense gamma-ray light, known as SGRBs. While the gamma rays last mere seconds, the optical light can continue for hours before fading below detection levels (an event called an afterglow). SGRBs are some of the most luminous explosions in the universe with, at most, a dozen detected and pinpointed each year. They currently represent the only way to study and understand a large population of merging neutron star systems.

Since

“This is the largest catalog of SGRB host galaxies to ever exist, so we expect it to be the gold standard for many years to come.”

– Anya Nugent, astrophysics graduate student

Prior to these new studies, astronomers characterized host galaxies from only a couple dozen SGRBs. The new catalog is quadruple the number of existing samples. With the advantage of a much larger dataset, the catalog shows that SGRB host galaxies can be either young and star-forming or old and approaching death. This means neutron-star systems form in a broad range of environments and many of them have quick formation-to-merger timescales. Because neutron-star mergers create heavy elements like gold and platinum, the catalog’s data also will deepen scientists’ understanding of when precious metals were first created in the universe.

“We suspect that the younger SGRBs we found in younger host galaxies come from binary stellar systems that formed in a star formation ‘burst’ and are so tightly bound that they can merge very fast,” Nugent said. “Long-standing theories have suggested there must be ways to merge neutron stars quickly, but, until now, we have not been able to witness them. We find evidence for older SGRBs in the galaxies that are much older and believe the stars in those galaxies either took a longer time to form a binary or were a binary system that was further separated. Hence, those took longer to merge.”

Potential of JWST

With the ability to detect the faintest host galaxies from very early times in the universe, NASA’s new infrared flagship observatory, the

“I started observations for this project 10 years ago, and it was so gratifying to be able to pass the torch onto the next generation of researchers,” Fong said. “It is one of my career’s greatest joys to see years of work come to life in this catalog, thanks to the young researchers who really took this study to the next level.”

References:

“Short GRB Host Galaxies. I. Photometric and Spectroscopic Catalogs, Host Associations, and Galactocentric Offsets” by Wen-fai Fong, Anya E. Nugent, Yuxin Dong, Edo Berger, Kerry Paterson, Ryan Chornock, Andrew Levan, Peter Blanchard, Kate D. Alexander, Jennifer Andrews, Bethany E. Cobb, Antonino Cucchiara, Derek Fox, Chris L. Fryer, Alexa C. Gordon, Charles D. Kilpatrick, Ragnhild Lunnan, Raffaella Margutti, Adam Miller, Peter Milne, Matt Nicholl, Daniel Perley, Jillian Rastinejad, Alicia Rouco Escorial, Genevieve Schroeder, Nathan Smith, Nial Tanvir and Giacomo Terreran, 21 November 2022, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ac91d0

“Short GRB Host Galaxies II: A Legacy Sample of Redshifts, Stellar Population Properties, and Implications for their Neutron Star Merger Origins” by Anya E. Nugent, Wen-Fai Fong, Yuxin Dong, Joel Leja, Edo Berger, Michael Zevin, Ryan Chornock, Bethany E. Cobb, Luke Zoltan Kelley, Charles D. Kilpatrick, Andrew Levan, Raffaella Margutti, Kerry Paterson, Daniel Perley, Alicia Rouco Escorial, Nathan Smith and Nial Tanvir, 21 November 2022, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ac91d1

The studies were supported by the National Science Foundation (award numbers AST-1814782 and AST-2047919), the David and Lucile Packard Foundation, the Alfred P. Sloan Foundation and the Research Corporation for Scientific Advancement.