Scientists trace origins of photons emitted by gamma ray bursts

Scientists in Japan have traced the origins of photons emitted by long duration gamma-ray bursts, the brightest electromagnetic events in the universe, to the visible portion of the relativistic jet produced by supernovae.

First discovered in 1967, long duration gamma-ray bursts, or GRBs, are extremely powerful explosions. For decades, scientists struggled to explain the high-energy events. Researchers eventually traced one type of GRB to the relativistic jets produced when massive stars die fiery deaths.

But until now, scientists weren't exactly sure how these jets spark GRBs.

Researchers at the RIKEN Cluster for Pioneering Research in Japan developed models to pinpoint the origins of the high-speed photons produced by GRBs. The team was able to measure the results of their simulations against an important new benchmark called the Yonetoku relation.

The Yonetoku relation describes a tight correlation between spectral peak energy and peak luminosity in GRB emissions.

With the Yonetoku relation as the standard, scientists used their simulations to test what's called the photospheric emission model. The model posits that GRB photons originate in the relativistic jet's photosphere. The quick expansion of the relativistic jet allows photons to escape.

To ensure the precision of their simulations, scientists replicated the complex dynamics of relativistic jets. The results showed the type of long duration gamma-ray bursts that escape the stellar envelope of an exploding massive star yielded the emissions correlation known as the Yonetoku relation.

Interactions between the dying star and relativistic jet naturally produced the Yonetoku relation.

"To us, this strongly suggests that photospheric emission is the emission mechanism of GRBs," Hirotaka Ito, scientist at the Cluster for Pioneering Research, said in a news release.

Ito and his colleagues published their findings Wednesday in the journal Nature Communications.

"While we have elucidated the origin of the photons, there are still mysteries concerning how the relativistic jets themselves are generated by the collapsing stars," Ito said. "Our calculations should provide valuable insights for looking into the fundamental mechanism behind the generation of these tremendously powerful events."

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