Chinese, Japanese Scientists Identify Potential Source of Ultrahigh-energy Cosmic Rays


BEIJING, March 3 (Xinhua) -- The Tibet ASgamma experiment, a China-Japan joint research project, has detected that a supernova remnant may be the source of some ultrahigh-energy cosmic rays.

Cosmic rays are high-energy particles that move through space at nearly the speed of light.

It is believed that particles could be accelerated in PeVatron and reach a petaelectron volt (PeV), which creates 100 times more energy than the record high achieved by any human-made accelerator on Earth.

Scientists have been trying to find these cosmic accelerators, hoping they could provide clues about how stars evolve and how energy is transported throughout the galaxy. No PeVatrons have been firmly detected yet.

The challenge in locating a PeVatron is that the direction in which a cosmic ray arrives is probably not the same as its source due to interstellar magnetic fields changing the trajectories of charged particles.

Fortunately, after being accelerated in PeVatron, cosmic rays may collide with nearby molecular clouds and produce gamma rays. Gamma rays, with no electric charge, can travel straight from their sources to Earth, and the observed arrival directions point back to their origins.

On Tuesday, a team of scientists from China and Japan reported in Nature Astronomy that they had identified supernova remnant SNR G106.3+2.7 as a potential PeVatron in our galaxy from the China-Japan Tibet ASgamma experiment.

According to the researchers, to identify an astrophysical source such as a PeVatron it must demonstrate the following three points simultaneously.

First, the source emits gamma rays up to and beyond 100 TeV (one-tenth of 1 PeV). Second, the gamma-ray emission region coincides with the location of a molecular cloud near the cosmic-ray accelerator. Third, it can be concluded that the ultra-high-energy gamma rays do not come from the high-energy electrons of pulsars.

In earlier observations, three observatories in the United States have pointed to SNR G106.3+2.7 as a possible accelerator of high energy cosmic rays, but it does not meet all three of the aforementioned conditions simultaneously.

The Tibet ASgamma experiment, located at an altitude of 4,300 meters above sea level in the town of Yangbajing in Tibet, has been operated jointly by China and Japan since 1990. In 2014, the project added new detectors which can significantly improve sensitivity.

Using data taken over two effective years, the research team observed ultrahigh-energy gamma rays up to and beyond 100 TeV from the SNR G106.3+2.7 and found that the center of the gamma-ray emission region is far away from the pulsar at the northeast corner of SNR G106.3+2.7 and in good agreement with the location of a nearby molecular cloud.

The researchers said that their work showed SNR G106.3+2.7 is a potential PeVatron in our galaxy, a big step in the attempt to reveal the mysterious origin of high energy cosmic rays.