Scientists at the New Jersey Institute of Technology (NJIT) have identified a specific source of high-energy gamma radiation linked to solar flares. The research, published in Nature Astronomy, details a class of energetic particles within the Sun's upper atmosphere that contribute to radiation signals observed during significant solar flare events. This discovery contributes to the understanding of solar flare physics and could inform models for space weather forecasting.
Discovery and Observations
The gamma-ray signals were traced to a localized region within the solar corona during an X8.2-class flare that occurred on September 10, 2017. Measurements indicated the presence of particles with energies of several million electron volts (MeV) in this region. These particles are hundreds to thousands of times more energetic than typical flare particles and travel at relativistic speeds.
Researchers propose that these high-energy particles generate gamma rays through a process called bremsstrahlung. Bremsstrahlung occurs when charged particles, such as electrons, emit high-energy light as they collide with material in the Sun's atmosphere.
Methodology and Particle Characteristics
The NJIT team, which includes scientists from NJIT's Center for Solar-Terrestrial Research (NJIT-CSTR), utilized observations from two primary instruments:
- NASA’s Fermi Gamma-ray Space Telescope: Provided data on gamma-ray emissions.
- NJIT's Expanded Owens Valley Solar Array (EOVSA): Supplied spatially resolved microwave imaging of accelerated particles in the solar corona.
Analysis of these combined datasets identified a distinct region, designated Region of Interest 3 (ROI 3), where both microwave and gamma-ray signals converged. This convergence indicated a population of particles energized to MeV levels.
Unlike typical solar flare electrons, which generally decrease in number with increasing energy, the identified particle population in ROI 3 exhibited a peak at higher energies, with a comparatively lower presence of lower-energy electrons. Advanced modeling connected the energy distribution of these particles to the observed gamma-ray spectrum, supporting bremsstrahlung emission as the source of the gamma-ray signals. Observations within ROI 3, located near areas of magnetic field decay and particle acceleration, align with existing theories concerning the acceleration and sustenance of energetic particles during solar flares.
Future Research
Further investigation is required to fully characterize these particle populations. A key question remains whether these high-energy particles are electrons or positrons. Future insights are anticipated from the upgraded EOVSA-15, a project funded by the National Science Foundation and led by NJIT-CSTR professor Bin Chen. This enhancement will provide the capability to measure the polarization of microwave emissions, which could help differentiate between electrons and positrons in these extreme particle populations.
The study, titled "Solar Flare Hosts MeV-peaked Electrons in a Coronal Source," received funding from the National Science Foundation and NASA. Gregory Fleishman, an NJIT-CSTR research professor of physics, served as the lead author of the study.