Abstract
This paper explores the characteristics of 42 solar X-class flares that were observed between February 2011 and November 2014, with data from the Solar Dynamics Observatory (SDO) and other sources. This flare list includes nine X-class flares that had no associated CMEs. In particular our aim was to determine whether a clear signature could be identified to differentiate powerful flares that have coronal mass ejections (CMEs) from those that do not. Part of the motivation for this study is the characterization of the solar paradigm for flare/CME occurrence as a possible guide to the stellar observations; hence we emphasize spectroscopic signatures. To do this we ask the following questions: Do all eruptive flares have long durations? Do CME-related flares stand out in terms of active-region size vs. flare duration? Do flare magnitudes correlate with sunspot areas, and, if so, are eruptive events distinguished? Is the occurrence of CMEs related to the fraction of the active-region area involved? Do X-class flares with no eruptions have weaker non-thermal signatures? Is the temperature dependence of evaporation different in eruptive and non-eruptive flares? Is EUV dimming only seen in eruptive flares? We find only one feature consistently associated with CME-related flares specifically: coronal dimming in lines characteristic of the quiet-Sun corona, i.e. 1 – 2 MK. We do not find a correlation between flare magnitude and sunspot areas. Although challenging, it will be of importance to model dimming for stellar cases and make suitable future plans for observations in the appropriate wavelength range in order to identify stellar CMEs consistently.
Highlights
Solar flares are among the most energetic phenomena in our solar system, and there continues to be a large international effort to understand the physical processes that release such vast amounts of energies in minutes
We studied seven questions that either come from preconceptions about large flares, or a physical expectation of how energy will be distributed in X-flares with or without Coronal mass ejections (CMEs)
Do large sunspot areas correspond to more powerful flares? In our sample, they do not, but averaged over an active-region lifetime, Sammis, Tang, and Zirin (2000) found a reasonable correlation
Summary
Solar flares are among the most energetic phenomena in our solar system, and there continues to be a large international effort to understand the physical processes that release such vast amounts of energies in minutes. The ever-improving observations have helped provide evidence (or otherwise) for a solar CME-associated flare model which assumes a twisted magnetic structure or flux rope rising in the corona, stressing the surrounding field lines and causing magnetic reconnection to occur; this would heat the local coronal plasma and accelerate the particles. This model as developed by Carmichael (1964), Sturrock (1966), Hirayama (1974) and Kopp and Pneuman (1976) ( CSHKP for short) appeared in the 1960s and 1970s and has since been extended. Both the pre-flare situation and the over-lying magnetic field strength and orientation appear to play key roles in determining whether or not a full eruption can occur
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