Scientists pinpoint gamma ray source in powerful solar flares
Researchers at the New Jersey Institute of Technology have uncovered a previously unknown source of intense gamma radiation generated during the sun's most powerful flares, solving a decades-old puzzle. Published January 7 in Nature Astronomy, these findings could enhance space weather forecasting and clarify how solar flares unleash their extreme energy.
The breakthrough identifies a newly detected class of high-energy particles in the sun's corona its upper atmosphere as the origin of gamma ray signals observed in major flares. These particles, reaching energies of several million electronvolts, prove hundreds to thousands of times more energetic than typical flare particles and travel near light speed.
"We knew solar flares produced a unique gamma ray signal, but those data alone couldn't reveal their source or generation mechanism," said lead author Gregory Fleishman, research professor of physics at NJIT's Center for Solar-Terrestrial Research. "By combining gamma ray and microwave observations from a solar flare, we've finally cracked this mystery."
The NJIT team analyzed a massive X8.2 flare from September 10, 2017, merging data from NASA's Fermi space telescope and NJIT's Expanded Owens Valley Solar Array radio telescope network in California. Their analysis pinpointed a distinct solar atmosphere region dubbed Region of Interest 3 where microwave and gamma signals overlapped, indicating a unique population of particles energized to millions of electronvolts.
Advanced modeling linked these particles' energy distribution directly to the observed gamma spectrum. Gamma rays arise from bremsstrahlung radiation, where charged particles emit high-energy light upon colliding with solar atmospheric matter.
Unlike typical flare-accelerated electrons, whose numbers drop as energy rises, this newfound population stands out with most particles at very high energies, Fleishman noted.
Key questions linger, such as whether these are electrons or positrons. Future insights may come from EOVSA-15, an upgrade to the Owens Valley array adding 15 new antennas and advanced ultra-wideband feeds. Led by NJIT physics professor Bin Chen, a co-author, the project receives National Science Foundation funding.
"Measuring polarization in microwave emissions from similar events could definitively distinguish them," Fleishman said. "We expect to gain that capability soon with the EOVSA-15 upgrade."
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