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Abstract Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare that occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a partial eruption of a twisted filament observed in Hαby the Goode Solar Telescope at the Big Bear Solar Observatory. The extreme ultraviolet (EUV) and X-ray signatures of the event are generally consistent with the standard scenario of eruptive flares, with the presence of double flare ribbons connected by a bright flare arcade. Intriguingly, this partial eruption event features a microwave counterpart, whose spatial and temporal evolution closely follow the filament seen in Hαand EUV. The spectral properties of the microwave source are consistent with nonthermal gyrosynchrotron radiation. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600 to 1400 Gauss from its apex to the legs. The results agree well with the nonlinear force-free magnetic model extrapolated from the preflare photospheric magnetogram. We conclude that the microwave counterpart of the erupting filament is likely due to flare-accelerated electrons injected into the filament-hosting magnetic flux rope cavity following the newly reconnected magnetic field lines.
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This content will become publicly available on April 23, 2026
Dynamic Motion of Microwave Bursts during a Solar Limb Flare
Abstract The SOL2013-10-28T02:02:58L133C110 flare occurred on the western limb, acquiring the GOES class of X1.0, and we focus on an oscillatory phenomenon detected at 34 GHz by the Nobeyama Radioheliograph (NoRH) during this flare. The oscillation is less obvious at 17 GHz and is unseen for a hard X-ray source detected by the RHESSI. In the 94 Å images from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we traced the evolution of the extreme ultraviolet (EUV) images capturing an eruption around 01:58 UT over the location of the RHESSI 50–100 keV source. We located the microwave emitting loop inferred from the 17/34 GHz maps within the complex EUV loop systems, and performed a model calculation of the dynamic evolution of the microwave brightness, including the radiative transfer in a magnetically asymmetric loop and evolving nonthermal electrons. The results demonstrate that a quasiperiodic injection of energetic electrons at a fixed spatial point is sufficient to reproduce such an oscillatory motion, without an actual shift of the nonthermal electron injection point, and that the magnetic environment required for the microwave loop model is consistent with the observed EUV activities related to the overall reconnection geometry.
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- Award ID(s):
- 2114201
- PAR ID:
- 10648206
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 984
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 39
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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