An international team of researchers has published in the journal Nature their discovery of the location of the source of the radio signal emitted from a class C solar flare more than 5,000 kilometers above the Sun’s surface. Communication. The findings could help scientists better understand the physical processes behind the release of energy from solar flares, the most powerful eruptions in the Solar System, the researchers say.

“The finding is unexpected,” said Siji Yu, the study’s corresponding author and an astronomer at NJIT’s Center for Solar-Terrestrial Studies. “This vibrational pattern is important for understanding how energy is released and dissipated in the Sun’s atmosphere during these incredibly powerful explosions in the Sun. However, the origin of these repetitive patterns, also called quasi-periodic vibrations, has long been a mystery and a concern among physicists. It has been a source of controversy.”

Solar radio bursts are intense bursts of radio waves from the Sun known to contain signals with repeating patterns often associated with solar flares. The team was able to identify the source of these signature signals after examining microwave observations from July 13, 2017, a solar flare captured by NJIT’s Expanded Owens Valley Solar Array (EOVSA) aboard Owens Valley Radio. Observatory (OVRO), near Big Pine, California.

EOVSA regularly observes the Sun over a wide microwave frequency range from 1 to 18 gigahertz (GHz) and is sensitive to radio emissions from high-energy electrons fed by solar flares in the Sun’s atmosphere. Lead author of the study, Ph.D. Student at Nanjing University (NJU).

The team detected a strong quasi-periodic pulsating (QPP) signal at the base of an electric current extending more than 25,000 kilometers through the flare region of the blast core, where opposing magnetic field lines converge, break, and reconnect, creating an intense electric current. the energy that powers the glow.

But surprisingly, Ku says they discovered a second heartbeat in the flash.

“Repeated patterns in solar radio bursts are not uncommon,” Coe said. “But interestingly, there’s a secondary source that we didn’t expect, located along the extended current table, that pulsates in a similar way to the main QPP source.”

“The signals likely originate from quasi-repetitive magnetic reconnections in the flash current layer,” Yu added. “This is the first case where a quasi-periodic radio signal located in the reconnection region has been detected. This finding could help us determine which of the two sources caused the other.” ”

Using EOVSA’s unique microwave imaging capabilities, the team was able to measure the energy spectrum of electrons from two radio sources in this event.

“EOVSA spectral imaging has given us a new spatial and temporal diagnosis of the non-thermal electrons of the flash. … We found that the distribution of high-energy electrons in the primary QPP source is in phase with that of the secondary QPP source in the electron flow table,” said Bin Chen, associate professor of physics at NJIT and co-author of the paper. “This is strong evidence that the two sources of QPP are closely related.”

Continuing their research, the team members, led by the paper’s other corresponding author and NJU astronomy professor Xin Cheng, combined 2.5D numerical simulations of the solar flare with observations of soft X-ray emission from solar flares observed by NOAA. The GOES satellite measures fluxes of soft X-ray radiation from the Sun’s atmosphere in two different energy ranges.

“We wanted to know how periodicity occurs on the current page,” Cheng said. “What physical process causes periodicity and how does it relate to the formation of QPP?”

The team’s analysis showed magnetic islands or bubble-like structures forming in the current layer that semi-periodically move toward the flare region.

“The appearance of magnetic islands in the long elongated current layer plays an important role in changing the rate of energy release during this eruption,” Cheng said. “Such a quasi-periodic process of energy release leads to the repetitive production of high-energy electrons, which appear as QPPs in the microwave and soft X-rays.”

Finally, Yu says the research results shed new light on an important phenomenon underlying the rewiring process that drives these explosive events.

“We finally pinpointed the origin of QPP in solar flares as a result of periodic reconnection in the flare current layer. This study proposes a review of previously reported interpretations of QPP events and their effects on solar flares.”