Scientists Found Photons in Mysterious Gamma-ray Bursts

Researchers from the RIKEN Cluster for Pioneering Research used simulations to reveal that the photons emitted by long gamma-ray bursts actually originate in the photosphere.

Gamma-ray bursts (GRBs) were first discovered in 1967 but the logical explanation of this phenomenon remained a mystery for quite some time post-discovery. Years and years of research led scientists to a conclusion that relativistic jets of matter released during the death of massive stars give birth to these long bursts. Having said that, the mechanism of their production is still unknown to humanity.

GRBs are regarded as the most powerful electromagnetic event of our universe because the amount of energy released by it in a second is equal to what our sun will release in its entire lifespan.   

Yonetoku Relation

The idea for this latest research came from a concept, called Yonetoku Relation, which was originally proposed by one of the authors of the study. This relation is between the peak luminosity of GRBs and the spectral peak energy. It is the strictest test for any model of GRB and provides the best possible explanation for the emission mechanism as it is easily the tightest correlation (identified so far) in the properties of Gamma-ray burst emission. In addition to that, it allows scientists to measure long distances by making use of GRBs. As a result, we can go further back into the past than type 1A supernovae which could provide us with some useful information about a number of mysteries including dark energy.

Photospheric Emission of Gamma-ray bursts

The researching team used different supercomputers, for simulations, in order to get the best possible results. Some popular ones among them were Hokusai (RIKEN), Aterui (National Astronomical Observatory of Japan), and Cray xc40 (Yukawa Institute for Theoretical Physics). In all these simulations, they primarily focused on the Photospheric Emission, a leading model for the emission mechanisms of GRBs. According to this model, the photons that we observe on the Earth are basically emitted from the photosphere of the relativistic jet. The expansion of the jet makes it easier for these photons to escape as light is scattered by fewer objects. Consequently, the place where it becomes possible for photons to escape moves downward through the jet.

Validating the Photospheric Emission Model

In order to test the validity of this model, the researchers combined the calculations of radiation transfer and the three-dimensional relativistic hydrodynamical simulations. By following this path, they evaluated Photospheric emissions from a relativistic jet and observed that the model worked absolutely fine, at least for the long GRBs. It also verified the idea that the Yonetoku Relation could be explained as a natural consequence of the jet-stellar interactions. Hirotaka Ito, a Member of the researching team from the Cluster for Pioneering Research, referred to that by saying,

“To us, this strongly suggests that photospheric emission is the emission mechanism of GRBs. 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. Our calculations should provide valuable insights for looking into the fundamental mechanism behind the generation of these tremendously powerful events.”