TY - JOUR
T1 - Observations of Extremely Strong Magnetic Fields in Active Region NOAA 12673 Using GST Magnetic Field Measurement
AU - Lozitsky, Vsevolod
AU - Yurchyshyn, Vasyl
AU - Ahn, Kwangsu
AU - Wang, Haimin
N1 - Funding Information:
We thank the referees for their careful reading of the manuscript and for providing valuable criticism and suggestions. BBSO operation is supported by NJIT and US NSF AGS-1821294 grants. GST operation is partly supported by the Korea Astronomy and Space Science Institute (KASI), Seoul National University. V.L.’s efforts were partly supported by the Taras Shevchenko National University, project 19BF023-03. V.Y. acknowledges support from NSF AST-1614457, AGS-1954737, AST-2108235, AFOSR FA9550-19-1-0040, NASA 80NSSC17K0016, 80NSSC19K0257, and 80NSSC20K0025 grants.
Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/3/1
Y1 - 2022/3/1
N2 - We present a detailed study of very strong magnetic fields in the NOAA Active Region (AR) 12673, which was the most flare productive AR in solar cycle 24. It produced four X-class flares including the X9.3 flare on 2017 September 6 and the X8.2 limb event on September 10. Our analysis is based on direct measurements of full Zeeman splitting of the Fe i 1564.85 nm line using all Stokes I, Q, U, and V profiles. This approach allowed us to obtain reliable estimates of the magnitude of magnetic fields independent of the filling factor and atmosphere models. Thus, the strongest fields up to 5.5 kG were found in a light bridge (LB) of a spot, while in the dark umbra magnetic fields did not exceed 4 kG. In the case of the LB, the magnitude of the magnetic field is not related to the underlying continuum intensity, while in the case of umbral fields we observed a well-known anticorrelation between the continuum intensity and the field magnitude. In this study, the LB was cospatial with a polarity inversion line of δ-sunspot, and we speculate that the 5.5 kG strong horizontal fields may be associated with a compact twisted flux rope at or near the photosphere. A comparison of the depth of the Zeeman π and σ components showed that in the LB magnetic fields are, on average, more horizontal than those in the dark umbra.
AB - We present a detailed study of very strong magnetic fields in the NOAA Active Region (AR) 12673, which was the most flare productive AR in solar cycle 24. It produced four X-class flares including the X9.3 flare on 2017 September 6 and the X8.2 limb event on September 10. Our analysis is based on direct measurements of full Zeeman splitting of the Fe i 1564.85 nm line using all Stokes I, Q, U, and V profiles. This approach allowed us to obtain reliable estimates of the magnitude of magnetic fields independent of the filling factor and atmosphere models. Thus, the strongest fields up to 5.5 kG were found in a light bridge (LB) of a spot, while in the dark umbra magnetic fields did not exceed 4 kG. In the case of the LB, the magnitude of the magnetic field is not related to the underlying continuum intensity, while in the case of umbral fields we observed a well-known anticorrelation between the continuum intensity and the field magnitude. In this study, the LB was cospatial with a polarity inversion line of δ-sunspot, and we speculate that the 5.5 kG strong horizontal fields may be associated with a compact twisted flux rope at or near the photosphere. A comparison of the depth of the Zeeman π and σ components showed that in the LB magnetic fields are, on average, more horizontal than those in the dark umbra.
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U2 - 10.3847/1538-4357/ac5518
DO - 10.3847/1538-4357/ac5518
M3 - Article
AN - SCOPUS:85128113841
SN - 0004-637X
VL - 928
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 41
ER -