Quasi-periodic pulsations (QPPs) are often detected in solar and stellar flares, but the underlying physical mechanisms have yet to be determined. In a new study, an international team of researchers has reported an unexpected discovery of a solar radioburst with a signal pattern similar to a heartbeat.
This heartbeat-like radio burst is located in the sun’s atmosphere.
After studying microwave observations of a solar flare event on July 13, 2017, captured by NJIT’s radio telescope called the Expanded Owens Valley Solar Array (EOVSA), which is located at Owens Valley Radio Observatory (OVRO), close to Big Pine, California, the team was able to determine the source of these pattern signals. The source location of a radio signal emanating from a C-class solar flare more than 5,000 kilometers above the surface of the sun.
Scientists noted, “The study’s findings may help scientists better understand the physical processes behind the energy release of solar flares — the solar system’s most powerful explosions.”
Sijie Yu, the study’s corresponding author and astronomer associated with NJIT’s Center for Solar-Terrestrial Research, said: “The discovery is unexpected. This beat pattern is important for understanding how energy is released and dispersed in the Sun’s atmosphere during these mighty explosions on the Sun. However, the origin of these repetitive patterns, known as quasi-periodic pulsations, has long been a mystery and a source of debate among solar physicists.”
The team detected a strong quasi-periodic pulsation signal (QPP) at the bottom of a stream sheet that stretched 15,000 miles through the eruption region, where opposing magnetic field lines approached, broke apart, and then reconnected to release the intense energy. who powered the torch.
Yuankun Kou, a Ph.D. student at Nanjing University (NJU), said: “From EOVSA’s observations of the flare, the team revealed radio flashes with a signal pattern that repeats every 10-20 seconds, ‘like a heartbeat’.
“But surprisingly, they discovered a second heartbeat in the torch.”
“The repeating patterns are not unusual for solar radiobursts. But interestingly, there is a secondary source we didn’t expect along the stretched current plate that pulsates similarly to the main QPP source.
Yu said, “The signals likely originate from quasi-repetitive magnetic reconnections on the flare current plate. This is the first time a quasi-periodic radio signal has been detected in the reconnect area. This detection can help us determine which of the two sources caused the other.”
In this case, the team detected the energy spectrum of electrons at the two radio sources using EOVSA’s special microwave imaging capabilities. The spectral imaging of EOVSA gave them new spatially and temporally resolved diagnostics of the flare’s non-thermal electrons.
Bin Chen, associate professor of physics at NJIT and co-author of the paper, said: “We found that the distribution of high-energy electrons in the main QPP source varies in phase with that of the secondary QPP source in the current electronic sheet. This strongly indicates that the two QPP sources are closely related.”
Corresponding author of the paper and professor of astronomy Xin Cheng at NJU combined 2.5D numerical modeling of the solar flare with soft X-ray observations of the solar flares observed by NOAA’s GOES satellite. The team wanted to know how the periodicity occurs in the current leaf.
asked Cheng, “What is the physical process driving the periodicity, and how is it related to the formation of the QPPs?”
The team’s research revealed that magnetic islands, or bubble-like structures, appear in the current leaf and move semi-periodically toward the area that is flaring.
Cheng said, “The appearance of magnetic islands in the elongated streamsheet plays a key role in adjusting the energy release rate during this outburst. Such a quasi-periodic energy release process leads to a repetitive production of high-energy electrons, which manifest as QPPs in the microwave – and soft X-ray wavelengths.”
Yu said, “Ultimately, the study’s findings shed new light on an important phenomenon underlying the reconnection process that drives these explosive events.”
“We finally pinpointed the origin of QPPs in solar flares through periodic reconnection in the flare flow sheet. This study leads to a re-examination of the interpretations of previously reported QPP events and their implications for solar flares.”
Magazine reference:
- Kou, Y., Cheng, X., Wang, Y. et al. Microwave imaging of quasi-periodic pulsations in flare flow sheet. Nat Commun 13, 7680 (2022). DOI: 10.1038/s41467-022-35377-0
