The highest-energy gamma rays discovered by the Tibet ASgamma experiment

The highest energy gamma rays discovered by the Tibet ASgamma experiment
The left figure shows the Tibet ASgamma experiment observed the highest energy gamma rays beyond 100 Teraelectron volts (TeV)from the Crab Nebula with low background noise, the cross mark indicates the Crab pulsar position. And the right figure shows the Crab Nebula taken by the Hubble Telescope Credit: NASA

The Tibet ASgamma experiment, a China-Japan joint research project, has discovered the highest energy cosmic gamma rays ever observed from an astrophysical source—in this case, the Crab Nebula. The experiment detected gamma rays ranging from > 100 Teraelectron volts (TeV) (Fig.1) to an estimated 450 TeV. Previously, the highest gamma-ray energy ever observed was 75 TeV by the HEGRA Cherenkov telescope.

Researchers believe the most energetic of the rays observed by the Tibet ASgamma experiment were produced by interaction between high-energy electrons and , remnant radiation from the Big Bang.

The Crab Nebula is a famous supernova remnant in the constellation Taurus. It was first observed as a very bright supernova explosion in1054 AD (see Fig.1). It was noted in official histories of the Song dynasty in ancient China as well as in Meigetsuki, written by the 12th century Japanese poet Fujiwara no Teika. In the modern era, the 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. The China-Japan collaboration added new water Cherenkov-type muon detectors under the existing cosmic-ray detectors in 2014 (see Fig.2). These underground muon detectors suppress 99.92 percent of cosmic-ray background noise (see Fig.3). As a result, 24 gamma-ray candidates above 100 TeV have been detected from the Crab Nebula with low background noise. The highest energy is estimated at 450 TeV (see Fig.2).

The highest energy gamma rays 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 display of the observed 449TeV photon-like air shower. Credit: IHEP

The researchers hypothesize the following steps for generating very-high-energy gamma rays: (1) In the nebula, electrons are accelerated up to PeV, i.e., peta (one thousand trillion) electron volts within a few hundred years after the supernova; (2) PeV electrons interact with the cosmic microwave background radiation (CMBR) filling the whole universe; (3) A CMBR photon is kicked up to 450 TeV by the PeV electrons. The researchers thus conclude that the Crab Nebula is now the most powerful natural electron accelerator discovered so far in our galaxy.

This pioneering work opens a new high-energy window for exploring the extreme universe. The detection of gamma rays above 100 TeV is a key to understanding the origin of very-high-energy cosmic rays, which has been a mystery since the discovery of cosmic rays in 1912. With further observations using this new window, we expect to identify the origin of cosmic rays in our galaxy, namely, pevatrons, which accelerate cosmic rays up to PeV energies.

The highest energy gamma rays discovered by the Tibet ASgamma experiment
The China-Japan collaboration placed new water Cherenkov-type muon detectors under the existing cosmic-ray air-shower array in 2014. These underground muon detectors can suppress 99.92% of cosmic-ray background noise. Credit: IHEP

"This is a great first step forward," said Prof. HUANG Jing, co-spokesperson for the Tibet ASgamma experiment. "It proves that our techniques worked well, and with energies up to a few hundred TeV really exist. Our goal is to identify a lot of pevatrons, which have not yet been discovered and are supposed to produce the highest-energy cosmic rays in our galaxy."


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Citation: The highest-energy gamma rays discovered by the Tibet ASgamma experiment (2019, July 3) retrieved 22 July 2019 from https://phys.org/news/2019-07-highest-energy-gamma-rays-tibet-asgamma.html
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Jul 03, 2019
The nature of the physical space seems the most important subject in physics. A present paper proceeds from the assumption of physical reality of space contrary to the standard view of the space as a purely relational nonexistence - void. The space and its evolution are the primary sources of phenomena in Mega- and micro-worlds. Thus cosmology and particle physics have the same active agent - physical space.
https://www.acade...osmology
https://www.acade...and_Jets

Jul 07, 2019
the standard view of the space ISN'T as a purely relational nonexistence

Jul 07, 2019
@shootie, very perceptive. Back in the day, that's how they saw it, but then they developed quantum field theory and realized that it implied that every possible quantum field theory implies that there is a multitude of fields in every little bit of spacetime. Even if the value is zero, there's still a field there. A lot of people have trouble with that; glad you don't.

"Empty space" ain't empty.

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