Microwave Zebra Pattern Structures in the X2.2 Solar Flare on Feb 15, 2011

TL;DR

This study analyzes microwave zebra pattern structures observed during the 2011 X2.2 solar flare, suggesting the double plasma resonance model explains their formation and estimating magnetic field strengths in the source regions.

Contribution

It provides the first detailed analysis of microwave ZPs during an X-class flare and supports the double plasma resonance model as the explanation for their formation.

Findings

High-frequency ZP observed at 7.00 GHz during flare rise

Two lower-frequency ZPs observed during decay phase

Estimated magnetic fields range from 23 to 345 G in source regions

Abstract

Zebra pattern structure (ZP) is the most intriguing fine structure on the dynamic spectrograph of solar microwave burst. On 15 February 2011, there erupts an X2.2 flare event on the solar disk, it is the first X-class flare since the solar Schwabe cycle 24. It is interesting that there are several microwave ZPs observed by the Chinese Solar Broadband Radiospectrometer (SBRS/Huairou) at frequency of 6.40 ~ 7.00 GHz (ZP1), 2.60 ~ 2.75 GHz (ZP2), and the Yunnan Solar Broadband Radio Spectrometer (SBRS/Yunnan) at frequency of 1.04 ~ 1.13 GHz (ZP3). The most important phenomena is the unusual high-frequency ZP structure (ZP1, up to 7.00 GHz) occurred in the early rising phase of the flare, and there are two ZP structure (ZP2, ZP3) with relative low frequencies occurred in the decay phase of the flare. By scrutinizing the current prevalent theoretical models of ZP structure generations, and comparing their estimated magnetic field strengths in the corresponding source regions, we suggest that the double plasma resonance model should be the most possible one for explaining the formation of microwave ZPs, which may derive the magnetic field strengths as about 230 - 345 G, 126 - 147 G, and 23 - 26 G in the source regions of ZP1, ZP2, and ZP3, respectively.