New Device Helps Unlock New Insights into Explosive Gamma-ray Bursts

Using a new, shoebox-sized device known as RINGO2, scientists successfully unlocked key details in the universe's brightest explosions: gamma-ray bursts (GRBs).

Most GRBs are thought to form when the nuclear combustion in a massive star's core comes to a halt, drained of fuel. As this happens, the star collapses under its own weight, forming a black hole that then pushes jets of particles through the collapsing star. When the particles escape, they erupt into space at close to the speed of light.

Everything from radio waves to gamma rays are emitted when the jet knocks up against its surroundings and begins to slow down, causing an outward-moving shock wave to form. Simultaneously, a reverse shock wave is created, driving the jet debris back and producing a bright emission of its own.

"One way to picture these different shocks is by imagining a traffic jam," Carole Mundell from the Astrophysics Research Institute at Liverpool John Moores University said in a statement. "Cars approaching the jam abruptly slow down, which is similar to what happens in the forward shock. Cars behind them slow in turn, resulting in a wave of brake lights that moves backward along the highway, much like the reverse shock."

According to scientists' theoretical models, the light formed in this reverse shock should exhibit stable polarized emissions in the case that the jet boasts a structured magnetic field derived from the area surrounding the infant black hole.

In the past, observations have detected polarizations of roughly 10 percent, but offered no clue as to how this varied over time.

On March 8, 2012, NASA's Swift satellite sensed a 100-second pulse of gamma rays coming from the constellation Ursa Minor, immediately forwarding the spacecraft's location to observatories around the globe.

The 2-meter Liverpool Telescope located in the Canary Islands responded immediately.

"Just four minutes after it received Swift's trigger, the telescope found the burst's visible afterglow and began making thousands of measurements," Mundell said.

The telescope was outfitted with RINGO2, developed by Mundell's team to probe the magnetic fields long believed to both drive and focus GRB jets, which went on to collect 5,600 photographs of the burst's afterglow while the magnetic field's properties were still encoded in its captured light.

According to initial observations, the afterglow light was polarized by a record 28 percent before slowly declining to 16 percent. Meanwhile, the angle of the polarized light stayed the same.

What this means is that, instead of a tangled magnetic field created by instabilities within the jet, a large and organized magnetic field appears to be linked to the black hole.

"This is a remarkable discovery that could not have occurred without the lickety-split response times of the Swift satellite and the Liverpool Telescope," said Neil Gehrels, the Swift principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md.

The study was published in the Dec. 5 issue of the journal Nature.