Gamma ray bursts (GRBs) are rare and only occur when extremely massive stars go supernova. The stars' strong magnetic fields channel most of the explosion's energy into two powerful plasma jets, one at each magnetic pole. The jets spray energetic particles at light speed for light-years in both directions.
On Earth, we detect the debris as gamma rays. Researchers also suspect - but haven't been able to prove - that GRBs are the source of at least some of the cosmic rays and neutrinos that pepper our planet from space.
Now, physicists at Ohio State University are using computer simulations to prove that theory. Their findings appear online in the journal Nature Communications. The study also raises new questions that can be answered only by the next generation of neutrino telescopes.
Mauricio Bustamante, a Fellow of the Center for Cosmology and AstroParticle Physics at Ohio State, explained that the new computer model is a result of recent findings in astroparticle physics, such as the first confirmed cosmic neutrinos detected at the IceCube Neutrino Observatory at the South Pole in 2013.
"Previously, the details of the non-uniformity of the GRB jets were not too important in our models, and that was a totally valid assumption - up until IceCube saw the first cosmic neutrinos a couple of years ago," Bustamante said, according to the press release. "Now that we have seen them, we can start excluding some of our initial predictions, and we decided to go one step further and do this more complex analysis."
With Philipp Baerwald and Kohta Murase of the Institute for Gravitation and the Cosmos at Pennsylvania State University and Walter Winter from the DESY national research center in Germany, Bustamante wrote new computer code to take into account the shock waves that are likely to occur within the jets. They simulated what would happen when blobs of plasma in the jets collided, and calculated the particle production in each region.
Bustamante explains in an analogy where the plasma jet is a long highway. "Everywhere on the highway there are fast-moving cars, but some of them will be fast sports cars, while others will be extra-fast Formula 1 racers," he said, according to the press release. "They will collide all over the highway, and when they do they will create debris. The debris always contains neutrinos, cosmic rays and gamma rays, but, depending on where the collisions occurred, one of these will typically dominate the emission."
"If the cars collide close to the beginning of the highway, where the concentration of cars is higher, the debris will be mostly neutrinos," Bustamante continued, according to the press release. "As they race along the highway, the concentration of cars goes down, and so when a collision occurs halfway through the length of the highway, the debris will be mostly cosmic rays. Further down the road, the concentration is even lower, and the gamma rays that we observe at Earth are produced in the collisions at this stage."
The amount of debris that reaches Earth depends on how energetic the star is and how far away it is.
"We expect that the next generation of neutrino telescopes, such as IceCube-Gen-2, will be sensitive to this minimal flux that we're predicting," Bustamante said, according to the press release. "Then astrophysicists can use the model to refine notions of GRB internal structure and better understand the sources of cosmic particles detected on Earth."
This work was funded by NASA, the German Research Foundation and the U.S. National Science Foundation.
