The Relationship between Solar Coronal X-Ray Brightness and Active Region Magnetic Fields: A Study Using High Resolution Hinode Observations

TL;DR

This study uses high-resolution Hinode observations to clarify the relationship between active region magnetic fields and coronal X-ray brightness, finding magnetic flux as the main determinant and no link to magnetic non-potentiality.

Contribution

It provides high-resolution observational evidence that magnetic flux primarily influences coronal X-ray brightness, challenging previous assumptions about non-potentiality's role.

Findings

Total X-ray brightness correlates with magnetic flux and current.

Magnetic flux is the main factor determining X-ray brightness.

No positive correlation between X-ray brightness and magnetic non-potentiality.

Abstract

By using high-resolution observations of nearly co-temporal and co-spatial Solar Optical Telescope spectropolarimeter and X-Ray Telescope coronal X-ray data onboard Hinode, we revisit the problematic relationship between global magnetic quantities and coronal X-ray brightness. Co-aligned vector magnetogram and X-ray data were used for this study. The total X-ray brightness over active regions is well correlated with integrated magnetic quantities such as the total unsigned magnetic flux, the total unsigned vertical current, and the area-integrated square of the vertical and horizontal magnetic fields. On accounting for the inter-dependence of the magnetic quantities, we inferred that the total magnetic flux is the primary determinant of the observed integrated X-ray brightness. Our observations indicate that a stronger coronal X-ray flux is not related to a higher non-potentiality of active-region magnetic fields. The data even suggest a slightly negative correlation between X-ray brightness and a proxy of active-region non-potentiality. Although there are small numerical differences in the established correlations, the main conclusions are qualitatively consistent over two different X-ray filters, the Al-poly and Ti-poly filters, which confirms the strength of our conclusions and validate and extend earlier studies that used low-resolution data. We discuss the implications of our results and the constraints they set on theories of solar coronal heating.