China's observatory LHAASO discovers very-high-energy diffuse Galactic gamma-ray emission

BEIJING -- A group of Chinese and international scientists conducted a high-precision measurement of the very-high-energy diffuse gamma-ray emissions from the Galactic plane using the data from China's Large High Altitude Air Shower Observatory (LHAASO), according to the Chinese Academy of Sciences (CAS) on Tuesday.

This is the most accurate measurement of its kind to date, and it is also the first measurement result provided for the Galactic plane covering Galactic longitudes from 15 degrees to 235 degrees and latitudes from minus five degrees to five degrees in an energy range of 1 to 25 TeV, the academy highlighted.

The diffuse Galactic gamma-ray emission is a very important tool used to study the propagation and interaction of cosmic rays in the Milky Way. Previously, observations from ground-based experiments at very-high-energy band were scarce.

LHAASO, located at an altitude of 4,410 meters on Mount Haizi in Daocheng county, Southwest China's Sichuan province, began regular operations in July 2021. It has since been recognized as a leading international facility with the world's highest sensitivity and accuracy for gamma-ray and cosmic-ray detection.

Combining the Square Kilometer Array (KM2A) measurements at higher energies, the scientists have achieved precise observations of the diffuse emission from the Galactic plane across an energy range spanning six orders of magnitude for the first time.

Along the Galactic longitude, the spatial distribution of the diffuse emission showed deviation from that of the gas column density, according to their research article published in the journal Physical Review Letters, adding that the spectral shape of the diffuse emission may vary in different longitude regions.

This observational result provided new insights into the exploration of cosmic-ray origins and propagation, as well as extreme astrophysical accelerators.