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The highly energetic gamma rays discovered by the Tibet ASgamma experiment



  The highest energy gamma ray detected by the Tibet ASgamma experiment
The left figure shows the Tibet ASgamma experiment observed the highest energy beams in excess of 100 Teraelectron volts (TeV) from the low background noise crab nebula, the cross mark indicates the crab's pulses position. And the right figure shows Crab Nebula taken by the Hubble Telescope Credit: NASA

The Tibet ASgamma experiment, a joint research project between China and Japan, has discovered the highest energy cosmic gamma rays ever observed from an astrophysical source – in this case the crab nebula. The experiment discovered gamma rays from> 100 Teraelectron Volts (TeV) (Fig. 1) to an estimated 450 TeV. Previously, the highest gamma ray energy ever observed was 75 TeV of the HEGRA Cherenkov telescope.


Scientists believe that the most energetic of the gamma rays observed by the Tibet ASgamma experiment was produced by interaction between high energy electrons and cosmic microwave background radiation, residual radiation from the Big Bang.

Crab Nebula is a famous supernova remnant in the constellation Taurus. It was first observed as a very light supernova explosion in 1054 AD (see Figure 1). It was recorded in official stories of the Song Dynasty of ancient China as well as in Meigetsuki, written by the 12th century Japanese poet Fujiwara no Teika. In modern times, Crab Nebula has been observed using various types of electromagnetic waves, including radio and optical waves, X-rays and gamma rays.

The Tibet ASgamma experiment has been operating since 1990 in Tibet, China, at an altitude of 4300 meters above sea level. China-Japan cooperation added new water Cherenkov-type muon detectors under the existing cosmic beam detectors in 2014 (see Figure 2). These underground muon detectors suppress 99.92 percent of cosmic-ray background noise (see Figure 3). As a result, 24 gamma ray candidates over 100 TeV have been detected from Krabbe Nebula with low background noise. The highest energy is estimated at 450 TeV (see Figure 2).

  The highest energy beams discovered by the Tibet ASgamma experiment
The left figure shows the Tibet ASgamma experiment (Tibet-III array + Muon Detector array); The right figure shows an event view of the observed 449TeV photon-like air shower. Credit: IHEP

The researchers hypothesize the following steps to produce very high-energy gamma rays: (1) In the nebula, the electrons are accelerated up to PeV, ie. poke (a thousand trillion) electron volts within a few hundred years after supernova; (2) PeV electrons interact with the cosmic microwave background radiation (CMBR) that fills the entire universe; (3) A CMBR photon is pushed up to 450 TeV of the PeV electrons. The researchers thus conclude that the crab nebula is now the most powerful natural electron accelerator that has so far been found in our galaxy.

This groundbreaking work opens a new window with high energy to explore the extreme universe. The detection of gamma rays above 100 TeV is a key to understanding the origin of very high-energy cosmic rays that have been a mystery since the discovery of cosmic rays in 1912. With further observations using this new window, we expect that Identify the origin of cosmic rays in our galaxy, namely pevrons, which accelerate cosmic rays up to PeV energies.

  The highest energy beams discovered by the Tibet ASgamma experiment
The cooperation between China and Japan added new water Cherenkov-type muon detectors during the existing cosmic-ray air-shower array in 2014. These underground muon detectors can suppress 99.92% cosmic-ray background noise. Credit: IHEP

"This is a good first step forward," said Professor HUANG Jing, the Tibet ASgamma experiment co-speaker. "It turns out that our techniques have worked well and gamma rays with energies up to a few hundred TeV really exist. Our goal is to identify many pevrons that have not yet been discovered and are supposed to produce cosmic rays of highest energy in our galaxies. "


Highest energy photons ever recorded come from crab nebula


Provided by
Chinese Academy of Sciences

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The highest energetic gamma rays discovered by the Tibet ASgamma experiment (2019, July 3)
July 3, 2019
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