According to a research published in The Astrophysical Journal recently, the magnetic field of the gamma-ray burst (GRB) can be effectively measured by the high-resolution spectral observation or the spectropolarimetric observation of the GRB optical absorption lines. The related physics can be strongly constrained by the results.

The research was led by Prof. MAO Jirong from Yunnan Observatories of the Chinese Academy of Sciences. The other collaborators are from South African Astronomical Observatory, University of the Free State, Brera Astronomical Observatory, and University College London.

GRB is the strongest explosion in the universe. This kind of object is very interesting for the research of both the high-energy astrophysics and the cosmology. The origin and the explosion mechanism are still under debate. It is difficult to measure magnetic field of high-energy celestial object by a direct way.

Polarization, which is the light propagating along a certain direction, is usually introduced to measure the magnetic field in the high-energy astrophysical field. Zeeman Effect, which is the triplet splitting of absorption lines in an optical spectrum, is also suggested to measure the magnetic field of the celestial objects in a direct way.

The South African Large Telescope (SLAT) is one of the largest optical/infrared telescopes in the world. Prof. MAO with his collaborators used the SALT to perform spectropolarimetric measurements to GRB 191221B. The polarization on the GRB optical absorption lines was investigated. In particular, the radiative transfer model of the GRB absorption lines was built by Prof. MAO and the collaborators. The polarization degree as a function of the magnetic field is presented. Thus, they obtained the magnetic field strength by the spectropolarimetry.

The ZeemanEffectis further proposed to observe the tripletstructurein the optical absorption lines by the high-resolution spectrographs.Therefore,researcherscan reveal the magnetic field properties of the GRB and thesurroundingmedium.High-resolution observation can be one vital issue for the future GRB research.

The results are important for the magnetic field measurement in the high-energy astrophysics. The results are also helpful to explore the GRB origin and evolution.

Contact:

MAO Jirong, Yunnan Observatories, CAS
Jirongmao@mail.ynao.ac.cn