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

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.

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Acknowledgements

Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as a domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in cooperation with ESA and the NSC (Norway). We are also grateful to Bruce Lites and the CSAC team for the Hinode/SP data. The Center of Excellence in Space Science India (CESSI) is supported by the Ministry of Human Resource Development, Government of India. SH is grateful to the Council for Scientific and Industrial Research, University Grants Commission, Government of India for financial support. DN acknowledges a Ramanujan Fellowship from the Department of Science and Technology and the (US) Asian Office of Aerospace Research and Development for financial support. Finally, we thank an anonymous referee, David E. McKenzie, Edward DeLuca, and the XRT team for critical comments and many useful discussions.

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Correspondence to Soumitra Hazra.

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Hazra, S., Nandy, D. & Ravindra, B. The Relationship Between Solar Coronal X-Ray Brightness and Active Region Magnetic Fields: A Study Using High-Resolution Hinode Observations. Sol Phys 290, 771–785 (2015). https://doi.org/10.1007/s11207-015-0652-9

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Keywords

  • Sun: activity
  • Sun: corona
  • Sun: magnetic fields
  • Sun: X-rays, gamma rays