On May 9, 2005, Swift detected a short burst, marking the first time for a short burst that astronomers detected an afterglow — something more common with longer bursts. “We had a hunch that short gamma-ray bursts came from a neutron star crashing into a black hole or another neutron star, but these new detections leave no doubt,” says Derek Fox, an astronomer at Pennsylvania State University. Fox’s team discovered the afterglow with NASA’s Chandra X-ray Observatory. The afterglow also was observed by a team led by Jens Hjorth of the University of Copenhagen using the Danish 1.5-meter telescope at La Silla Observatory in Chile.
Another short GRB was spotted July 9 with HETE-2. According to George Ricker of the Massachusetts Institute of Technology in Cambridge, “The July 9 burst was like the dog that didn’t bark. Powerful telescopes detected no supernova as the GRB faded, arguing against the explosion of a massive star. Also, the July 9 burst, and probably the May 9 burst, are located in the outskirts of their host galaxies, just where old merging binaries are expected.”
So after 35 years, a key piece of the puzzle about GRBs appears solved.