The Statistical Relationship between White-light Emission and Photospheric Magnetic Field Changes in Flares

Abstract

Continuum emission, also called white-light emission (WLE), and permanent changes of the magnetic field ($\Delta B_{\mathrm{LOS}}$) are often observed during solar flares. But their relation and their precise mechanisms are still unknown. We study statistically the relationship between $\Delta B_{\mathrm{LOS}}$ and WLE during 75 solar flares of different strengths and locations on the solar disk. We analyze SDO/HMI data and determine for each pixel in each flare if it exhibited WLE and/or $\Delta B_{\mathrm{LOS}}$. We then investigate the occurrence, strength, and spatial size of the WLE, its dependence on flare energy, and its correlation to the occurrence of $\Delta B_{\mathrm{LOS}}$. We detected WLE in 44/75 flares and $\Delta B_{\mathrm{LOS}}$ in 59/75 flares. We find that WLE and $\Delta B_{\mathrm{LOS}}$ are related, and their locations often overlap between 0-60\%. Not all locations coincide, thus potentially indicating differences in their origin. We find that the WL area is related to the flare class by a power law and extend the findings of previous studies, that the WLE is related to the flare class by a power law, to also be valid for C-class flares. To compare unresolved (Sun-as-a-star) WL measurements to our data, we derive a method to calculate temperatures and areas of such data under the black-body assumption. The calculated unresolved WLE areas improve, but still differ to the resolved flaring area by about a factor of 5-10 (previously 10-20), which could be explained by various physical or instrumental causes. This method could also be applied to stellar flares to determine their temperatures and areas independently.

arXiv commentAccepted for publication in ApJ

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