Afterglow alerts astronomers to gamma-ray burst

BALTIMORE — An incredibly energetic explosion in the cosmos has been discovered via its not-so-energetic afterglow. Each year, astronomers observe several hundred of these explosions, known as gamma-ray bursts, but this marks the first time they spotted a burst’s remnant radiance before detecting the burst itself. The finding, reported April 12 at a meeting of the American Physical Society, could enable the detection of other bursts whose high-energy signatures elude space telescopes.

A small fraction of gargantuan stars end their lives in spectacular explosions that send a narrow beam of gamma rays, the universe’s highest energy radiation, darting through space. Specialized space telescopes typically identify these bursts by detecting sudden flashes of gamma rays. But in February 2014, a 1.2-meter telescope in southern California spotted a visible-light flash that brightened dramatically within about an hour, which fits the profile of a burst’s afterglow. Sure enough, the next day astronomers looked back at data collected from three satellites and found a surge of gamma rays consistent with a burst.

Study coauthor Brad Cenko of the NASA Goddard Space Flight Center in Greenbelt, Md., says the next step is detecting “orphan” afterglows of bursts whose gamma-ray beams are not quite pointed toward Earth. Routinely detecting these orphans would increase the annual inventory of gamma-ray bursts by up to 100 times, giving astronomers more opportunities explore details about how these ultrabright explosions occur.