Spotting a Distant Afterglow

Editor’s note: AAS Nova is on vacation until 2 November. Normal posting will resume at that time; in the meantime, we’ll be taking this opportunity to look at a few interesting AAS journal articles that have recently been in the news or drawn attention.

As their name suggests, short gamma-ray bursts are very brief flashes of high-energy light that last less than a couple seconds — making them challenging to localize to their galaxy of origin. If you’re quick enough, however, you might be able to spot the faint but longer-lived afterglow in lower-energy wavelengths that follows the gamma-ray flash. And if you’ve got a powerful enough telescope, you might be able to spot this afterglow even when the explosion occurred ten billion light-years away!

Such is the case in a recent study led by Kerry Paterson (CIERA, Northwestern University), which announces the afterglow detection and localization of GRB 181123B using the Gemini North and Keck telescopes. GRB 181123B’s host galaxy lies at a redshift of z = 1.77, which corresponds to a time when the universe was just 3.8 billion years old! This is the second-most distant short gamma-ray burst we’ve pinpointed, and the most distant to also have an optical afterglow detected — providing a rare opportunity to study the mergers of neutron stars at “cosmic high noon”, when our young universe reached its peak period of star formation.

Check out the NOIRLab-produced video below for an artist’s illustration that shows how GRB 181123B compares to other gamma-ray bursts we’ve discovered so far.

Original article: “Discovery of the Optical Afterglow and Host Galaxy of Short GRB 181123B at z = 1.754: Implications for Delay Time Distributions,” K. Paterson et al 2020 ApJL 898 L32. doi:10.3847/2041-8213/aba4b0
CIERA press release and links to other resources: Short Gamma Ray Burst Leaves Most-distant Optical Afterglow Ever Detected