Abstract
ABSTRACT We study the decay phase of solar flares in several spectral bands using a method based on that successfully applied to white light flares observed on an M4 dwarf. We selected and processed 102 events detected in the Sun-as-a-star flux obtained with SDO/AIA images in the 1600 and 304 Å channels and 54 events detected in the 1700 Å channel. The main criterion for the selection of time profiles was a slow, continuous flux decay without significant new bursts. The obtained averaged time profiles were fitted with analytical templates, using different time intervals, that consisted of a combination of two independent exponents or a broken power law. The average flare profile observed in the 1700 Å channel decayed more slowly than the average flare profile observed on the M4 dwarf. As the 1700 Å emission is associated with a similar temperature to that usually ascribed to M dwarf flares, this implies that the M dwarf flare emission comes from a more dense layer than solar flare emission in the 1700 Å band. The cooling processes in solar flares were best described by the two exponents model, fitted over the intervals t1 = [0, 0.5]t1/2 and t2 = [3, 10]t1/2, where t1/2 is time taken for the profile to decay to half the maximum value. The broken power-law model provided a good fit to the first decay phase, as it was able to account for the impact of chromospheric plasma evaporation, but it did not successfully fit the second decay phase.
Highlights
Flares are explosive events that occur in solar and stellar atmospheres
This article aims to investigate the solar-stellar flare connection, and emission mechanisms associated with white light flares by comparing the flare profile associated with various layers of the Sun’s lower atmosphere with the flare profile associated with white light observations of flares on an M dwarf obtained by Davenport et al (2014)
We focused our study on the fitting of the averaged time profiles with models consisting of two components only, as done in previous studies
Summary
Flares are explosive events that occur in solar and stellar atmospheres. Flares are observed across a wide range of wavelengths, such as radio, visible, X-rays and gamma rays and the emission responsible for these observations originates from many different regions within solar and stellar atmospheres, from photospheres to coronae. It is generally believed that both solar and stellar flares are produced by the same mechanism, namely magnetic reconnection (Shibata & Magara 2011). Discrepancies are readily observed, most notably the energy of the flares, which, for stellar flares, can often be several orders of magnitudes larger than even the largest solar flares. While stellar flares have been studied for decades, it is only recently, through observations made by NASA’s Kepler mission (Borucki et al 2010), that a statistically large sample of flares for a single star has been obtained.
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