Scientists have seen the ins and outs of a gamma-ray burst for the first time—recognized its spectral lines

Supernova explosions, mergers of neutron stars and black holes give rise to the most energetic phenomena in the Universe – gamma-ray bursts, which are noticed on Earth only when caught in their rays. In October 2022, an extraordinary event occurred – the brightest gamma-ray burst in the entire history of observations, called BOAT. The burst blinded the telescope sensors, but did not prevent the recovery of the data, which turned out to be a surprise for scientists – a spectrum was discovered in them.

Image source: Science China Physics, Mechanics & Astronomy

On Thursday, July 25, 2024, two independent articles were published simultaneously in leading American and Chinese scientific journals, which spoke of an amazing discovery that caused “goosebumps” for scientists. For the first time in many years of recording gamma-ray bursts, a spectrum was discovered in it. More precisely, the signs of the spectra were present in gamma-ray bursts before, but they were all explained by interference. In the case of the BOAT event (registration number GRB 221009A), the probability of the appearance of interference rather than spectrum was estimated as one in 500 million. In other words, there is every reason to believe that scientists examined spectral lines for the first time as part of a gamma-ray burst.

To understand, the spectrum is the ins and outs of the physics and chemistry of the process. From absorption or glow lines, you can learn a lot about the phenomenon, which will allow you to speak with confidence about the origin of a particular gamma-ray burst. Scientists are not yet ready to speculate about the essence of the BOAT or “Brightest Of All Time” event, but decoding and modeling will continue, and this will become the basis for work on other similar phenomena.

One suspects that a significant contribution to this amazing discovery was made by Chinese scientists and the Chinese orbiting X-ray telescope GECAM-C. At the time of the BOAT event, all gamma-ray telescopes were blinded, including NASA’s flagship instrument, Fermi. In terms of intensity, the BOAT burst was on average 1000 times brighter than usually recorded bursts. The telescope sensors could not handle this, with the exception of the Chinese GECAM-C sensors, which were either partially disabled or set to lower sensitivity. Thanks to GECAM-C data, it was possible to reconstruct the Fermi data and isolate spectral lines from the signal.

The cover of the journal Science China Physics, Mechanics & Astronomy dedicated to the article.

According to the findings of an international team of scientists, the spectral emission lasted about 40 seconds and reached a peak energy of about 12 MeV, compared to 2 or 3 MeV for visible light. Chinese scientists have further characterized the flare’s spectral components, announcing the discovery of a gamma-ray line with energies up to 37 MeV, which they claim is the highest energy spectral line ever emitted by a celestial object in the Universe. By the way, signs of unusual physics were discovered in the BOAT event. The intrigue remains. I wonder what it could be?