Signatures of Confined and Eruptive Solar Flares in Microwave Spectra
Journal Article
Overview
abstract
Abstract; ; We describe how microwave spectra of confined flares differ from those of eruptive flares. All 29 confined ≥M1.4 soft X-ray flares from NOAA Active Region 12192 in 2014 October that were observed by the Radio Solar Telescope Network in the >300 MHz microwave range (encompassing RSTN frequencies from 410 to 15,400 MHz) had low-frequency (≥410 MHz) cutoffs in their peak-flux-density spectra, with peak emission <10 solar flux units (sfu) at 410 MHz. Wind/Waves observations at 1 MHz for 20 of these cutoff microwave bursts suggest that few, if any, of the 29 flares were accompanied by escaping electrons. We find a marked difference between microwave spectra for samples of intense (≥M5) confined and eruptive flares from 2011 to 2016: 20 of 21 confined ≥M5 flares had cutoff spectra, while 27 of 30 ≥M5 eruptive flares had peak 410 MHz emission >10 sfu (with a median value of 431 sfu). For the subsets of these events with Wind/Waves observations, only one of 20 confined events was unambiguously accompanied by 1 MHz emission, while 25 of the 29 eruptive flares had peak 1 MHz fluxes >10; 3; sfu (above a background of ∼200–400 sfu), with an overall median peak value of ∼10; 5; sfu. These results indicate that strong confined flares characteristically do not involve or affect open field lines, ruling out interchange reconnection as a confined-flare generation mechanism, leaving reconnection between closed loops as the likely alternative. The microwave spectral signatures of confined and eruptive flares have potential application for the determination of confinement/eruption for flares on solar-type stars.;
