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Published December 1, 2025 | Version Published
Journal Article Open

Enigmatic Centi-SFU and mSFU Nonthermal Radio Transients Detected in the Middle Corona

Creators

  • 1. ROR icon New Jersey Institute of Technology
  • 2. Cooperative Programs for the Advancement of Earth System Science, University Corporation for Atmospheric Research, Boulder, CO, USA
  • 3. ROR icon Jet Propulsion Lab
  • 4. ROR icon Arizona State University
  • 5. ROR icon California Institute of Technology
  • 6. ROR icon George Mason University
  • 7. ROR icon University of New Mexico
  • 8. Real-Time Radio Systems Ltd, Bournemouth, Dorset BH 6 3LU, UK
  • 9. ROR icon Rice University

Abstract

Decades of solar coronal observations have provided substantial evidence for accelerated particles in the corona. In most cases, the location of particle acceleration can be roughly identified by combining high spatial and temporal resolution data from multiple instruments across a broad frequency range. In almost all cases, these nonthermal particles are associated with quiescent active regions, flares, and coronal mass ejections (CMEs). Only recently, some evidence of the existence of nonthermal electrons at locations outside these well-accepted regions has been found. Here, we report for the first time multiple cases of transient nonthermal emissions, in the heliocentric range of ∼3–7 R ⊙ , which do not have any obvious counterparts in other wave bands, like white-light and extreme ultraviolet. These detections were made possible by the regular availability of high dynamic-range low-frequency radio images from the Owens Valley Radio Observatory's Long Wavelength Array. While earlier detections of nonthermal emissions at these high heliocentric distances often had comparable extensions in the plane of sky, they were primarily associated with radio CMEs, unlike the cases reported here. Thus, these results add on to the evidence that the middle corona is extremely dynamic and contains a population of nonthermal electrons, which is only becoming visible with high dynamic-range low-frequency radio images.

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

S.M., B.C., and D.G. acknowledge support by the NASA Living With a Star (LWS) Science grant 80NSSC24K1116. S.Y. was supported by the NASA Early Career Investigator Program (ECIP) grant to NJIT (80NSSC21K0623). P.Z. acknowledges support for this research by the NASA Living with a Star Jack Eddy Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award 80NSSC22M0097. The OVRO-LWA expansion project was supported by NSF under grant AST-1828784. OVRO-LWA operations for solar and space weather sciences are supported by NSF under grant AGS-2436999. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). A portion of this work was supported by the National Science Foundation Graduate Research Fellowship under grant No. 2139433. The authors also thank the referee for the comments, which have helped to improve the manuscript.

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Additional details

Funding

NASA ∣ SMD ∣ Heliophysics Division
80NSSC24K1116
NASA ∣ SMD ∣ Heliophysics Division
80NSSC21K0623
UCAR, Cooperative Programs for the Advancement of Earth System Science
80NSSC22M0097
NSF ∣ BFA ∣ Large Facilities Office
AST- 1828784
NSF ∣ Directorate for Geosciences
AGS-2436999

Caltech Custom Metadata

Caltech groups
Astronomy Department , Division of Physics, Mathematics and Astronomy (PMA) , Owens Valley Radio Observatory , Physics Department
Publication Status
Published