Are there Radio-quiet Solar Flares?

Abstract

Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 - 4000 MHz range (type I - V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800'' from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet > 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800'') without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source.

arXiv commentSolar Physics, in press

References in corpus (2)

• Are Heating Events in the Quiet Solar Corona Small Flares? - Multiwavelength Observations of Individual Events
• Survey on solar X-ray flares and associated coherent radio emissions

Cited by in corpus (6)

• A Review of Solar Type III Radio Bursts
• The Low-High-Low Trend of Type III Radio Burst Starting Frequencies and Solar Flare Hard X-rays
• Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer
• Densities Probed by Coronal Type III Radio Burst Imaging
• Coronal type III radio bursts and their X-ray flare and interplanetary type III counterparts
• A tiny event producing an interplanetary type III burst