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NJU Supernova Remnant Research Group Contributes to Identifying Potential Source of Ultrahigh-energy Cosmic Rays
Pubdate: 2021-03-11

On March 2nd,2021, 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 ASγ; experiment. The discovery sheds light on the knotty problem of the origin of cosmic rays (CRs). Researchers from the School of Astronomy and Space Science at Nanjing University were deeply involved in this important achievement, among whom Dr. Xiao Zhang is one of the six co-corresponding authors.

The Tibet ASγ; experiment, located at an altitude of 4,300 meters above sea level in the town of Yangbajing in Tibet serves as a world-famous instrument searching for PeVatron. 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 centroid position 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.

Fig. 1: Significance map around SNR G106.3+2.7 as observed by Tibet AS+MD above 10 TeV.

Fig. 2: The best-fit gamma-ray energy spectrum of SNR G106.3+2.7 in the leptonic (left) and hadronic (right) model.

Based on the aforementioned results, Dr. Zhang Xiao, PhD student Yiwei Bao and Professor Yang Chen from NJU conducted related spectral analysis and theoretical calculations. They pointed out that the leptonic scenario due to pulsar wind nebula is difficult to simultaneously explain the spatial morphology of GeV and TeV gamma-rays and the energy budget of leptons. While the observational results can be explained by the hadronic model if the diffusion coefficient around SNR is effectively suppressed by the self-exited turbulence of the CRs. Furthermore, an X-ray flux upper limit on the synchrotron spectrum would provide important information to firmly establish the hadronic scenario as the acceleration mechanism of particles at the source.

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