Professor LIN Jun from the Solar Activity and CME Theory group of Yunnan Observatories of Chinese Academy of Sciences, participated in a study led by Professor CHEN Bin of the New Jersey Institute of Technology. The international group conducted the radio observation of the magnetic field distribution and relativistic electron acceleration characteristics in the current sheet of solar flares. The related research results were published in the journal Nature Astronomy on July 27, 2020.
Solar eruption is the most violent energy release process in the solar system, which is usually accompanied by solar flares and coronal mass ejections (CMEs). In the standard flare model, the large-scale current sheet of magnetic reconnection is considered as the core engine of driving the rapid release of the magnetic energy and the particle acceleration.
However, due to lack of observations on the magnetic field property and high-energy particles near the current sheet, the key question such as the location and the mechanism of energy release and particle acceleration in solar flares is still open.
CHEN Bin et al. analyzed the microwave radiation near the current sheet in an X-class flare event on September 10, 2017 by using the Expanded Owens Valley Solar Array (EOVSA) data and the numerical experiment based on the Lin-Forbes model developed by Professor LIN Jun et al.
Lin-Forbes model is a theoretical solar eruption model for quantitative descriptions of the overall evolution in the magnetic field structure and its physical relation to magnetic reconnection during solar eruptive process. It is often used by researchers in the solar physics community to help interpret the observational phenomena, reveal the corresponding physical scenario and understand the physics behind it.
The research group found that the magnetic field in the current sheet shows a local maximum at the X-point of magnetic reconnection, and a local minimum in the region between the bottom of the current sheet and the top of the flare loop (also known as the magnetic bottle). The microwave energy spectrum shows that the acceleration or accumulation of more than 99% relativistic electrons are likely to occur in the magnetic bottle region at the top of the flare loop, rather than near the reconnecting X-point.
These results not only provide direct observational evidence for solving the problem of particle acceleration in the solar eruptive process, but also confirm the Lin-Forbes model.
The finding is the fruit of good international academic collaboration. At the time when Professor CHEN Bin and his collaborators started to carry out the above investigations, Professor LIN Jun was on a one-month visit to the Harvard- Smithsonian Center for Astrophysics (CfA).
In the communication with colleagues of CfA, Professor LIN learned about the work being carried out by Professor CHEN Bin from Dr. SHEN Chengcai and Katharine Reeves (co-authors of the above work). Professor CHEN invited LIN and SHEN to have a telecom for detailed discussions about topics of related work he was conducting and the Lin-Forbes model. These topics include the theoretical position of the magnetic reconnection X-point, the characteristics of plasma and magnetic field motions and the region where energetic particles are most likely to be accelerated.
Later, Professor CHEN invited Professor LIN to work together on the field mentioned above, Professor LIN accepted the invitation and joined Professor CHEN’s team, and got the job done eventually altogether.
It is a good example of international academic collaboration which is very important for scientific researches.
Contact:
LIN Jun, Yunnan Observatories, Chinese Academy of Sciences
jlin@ynao.ac.cn
