After nearly 50 years of waiting, scientists have finally directly witnessed a gamma ray burst, in an explosion which has set the record for the brightest light ever witnessed by humanity.
A team of scientists, which included two scientists from Nainital-based Aryabhatta Institute of Research in Observational Science (ARIES), has claimed to have discovered the highest energy photons from a Gamma Ray Burst (GRB) that emerged from the explosion of a star nearly 4.5 billion years ago. These findings shed light on how these extraordinary explosions happen, and how they can reshape the universe, researchers said. The burst is followed by a longer lasting afterglow mostly in the optical and X-ray spectral regions whose intensity decreases rapidly. Whilst these space-borne observatories have detected a few photons with even higher energies, the question if very-high-energy (VHE) gamma radiation (at least 100 billion times more energetic than visible light and only detectable with ground-based telescopes) is emitted, has remained unanswered until now.
It was emitted by a gamma ray burst seven billion light-years away and created extra vitality in just a few seconds than the solar will burn in its 10 billion yr lifetime. The team used the new MeerKAT radio telescope in South Africa to record the emission, which is at the opposite end of the spectrum compared to very high energy gamma rays.
The first of the two cosmic explosions - dubbed GRB 180720B - was detected by the the High-Energy Stereoscopic System (HESS) telescope in Namibia in July 2018.
Gamma ray bursts (GRBs), energetic jets of gamma rays that come from black holes, might be created in two other ways - leading to lengthy or quick GRBs. While the detection of GRBs at these very-high-energies had always been anticipated, the discovery many hours after the initial event, deep in the afterglow phase, came as a real surprise.
The radiation flowing from the GRB boats some of the highest energies astronomers have ever seen. The experiment was done in collaboration with scientists of 20 countries. If this jet is pointing towards Earth, we can see it as a bright gamma-ray burst, which typically lasts no more than a minute or two.
Dr Anderson said the high-energy light was likely caused by the blast wave of material from the gamma ray burst hitting the surrounding environment. Elementary particles are accelerated in these jets to velocities almost as high as the speed of light and interact with the surrounding matter and radiation, leading to the copious production of gamma rays.
"However, these photons are not able to reach the very high energies observed", she said. Most probably, the shock wave of the explosion acts here as the cosmic accelerator.
Analyzing the measurements from the first tens of seconds after the burst, astronomers found photons with energies of trillions of electronvolts - that's trillions of times the energy of the typical photons coming from the sun.
The very high-energy gamma rays are given off by matter that is accelerated to very close to the speed of light as it whirls around the black hole. The H.E.S.S results strongly constrain the emission to two potential mechanisms.
"MeerKAT is a new radio observatory with very good sensitivity", Dr. van der Horst said.
Because the bursts are rare and don't last long, it can be hard to get a good look at one with a telescope. This collaborative effort allowed an global team to gather an unprecedented level of information about GRB 190114C, capturing the evolution of the gamma-ray burst afterglow emission across 17 orders of magnitude in energy. Thanks to this GRB and the lessons learnt, our recently improved observational strategy has already payed off. As highlighted by Edna Ruiz Velasco, PhD. student at MPIK in Heidelberg and one of the corresponding authors of the publication: "This detection has already revolutionised the way we search for GRBs with Cherenkov Telescopes".