BEIJING -- China's cosmic ray observatory has detected ultra-high-energy gamma-ray radiation from the tail region of a pulsar, indicating a robust particle acceleration process in this area, according to the Institute of High Energy Physics under the Chinese Academy of Sciences.

The Large High Altitude Air Shower Observatory (LHAASO) made a groundbreaking observation by capturing the gamma-ray radiation from the tail region of the bow-shock pulsar wind nebula associated with the pulsar PSR J1740+1000, marking the first detection of such radiation from the tail of a bow-shock pulsar wind nebula.

The research, conducted by the LHAASO collaboration led by the institute, was published in the academic journal The Innovation.

Pulsars, rapidly rotating neutron stars, are named for their continuous emission of electromagnetic pulse signals. As pulsars age and their rotational energy diminishes, the number and maximum energy of high-energy particles in their nebulae decrease. However, particles previously accelerated by the pulsar can spread out, forming gamma-ray halos extending up to hundreds of light-years.

Some pulsars interact directly with the interstellar medium. Due to the pulsar's supersonic motion, a bow-shock pulsar wind nebula, resembling a "comet-like" structure, is formed. While the tail radiation of such nebulae has been observed in radio and X-ray bands, gamma-ray radiation from these regions had remained undetected until now.

The pulsar PSR J1740+1000 observed by LHAASO is a middle-aged pulsar located 4,500 light-years from the Earth, with a characteristic age of 110,000 years, and features a comet-shaped bow-shock pulsar wind nebula.

After more than three years of observation, the research team discovered a point-like ultra-high-energy gamma-ray source about 16 light-years from the pulsar. Remarkably, the source lies precisely along the extension of the bow-shock pulsar wind nebula tail, revealing that the tail region of a bow-shock pulsar wind nebula can produce ultra-high-energy gamma-ray radiation.

Traditional theories suggest that the energy of middle-aged pulsars declines, making it difficult for high-energy radiation to be produced in the tail region, said Chen Songzhan, a researcher at the institute.

Chen explained that the detection of ultra-high-energy gamma-ray radiation this time implies that the tail region of the bow-shock pulsar wind nebula possesses an extraordinary capability to accelerate particles to peta-electronvolt levels of energy.

LHAASO is located at an altitude of 4,410 meters on Mount Haizi in Daocheng county, Sichuan province, Southwest China. It began regular operation in July 2021 and is recognized as a leading international facility for gamma-ray and cosmic-ray detection.

The LHAASO collaboration has achieved significant results in multiple areas of physics based on its experimental data. This discovery represents another major accomplishment in gamma-ray astronomy for LHAASO.