Nonlinear Force-Free Field Modeling of a Three-Dimensional X-ray Sigmoid Observed on the Sun

Details Nonlinear Force-Free Field Modeling of a Three-Dimensional X-ray Sigmoid Observed on the Sun Nonlinear Force-Free Field Modeling of a Three-Dimensional X-ray Sigmoid Observed on the Sun

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh43b1950i&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH43B-1950

Astronomy and Astrophysics

Astrophysics

[7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7529] Solar Physics, Astrophysics, And Astronomy / Photosphere

Scientific paper

Three-dimensional (3D) structure of X-ray sigmoid has not been well understood in spite of many 2D observations obtained by satellites. Because a sigmoid is considered as a precursor causing huge solar flares, the 3D structure is a key issue to understand a trigger process for the solar flares. In this paper, we will report a 3D structure of an X-ray sigmoid of the solar active region NOAA 10930 using the Nonlinear Force-Free Field (NLFFF) modeling. Especially, we compare the X-ray emission with field-aligned current in the chromosphere and the twist of the magnetic field line estimated from the NLFFF. According to our analysis, the sigmoid is composed of field lines with a wide range of twist (0< |Tn| < 1.5) that satisfy a stable condition against Kink mode instability (|Tn| > 1.75 from Torok et al. 2004). The strong electric current is distributed on the strong X-ray intensity region corresponding to the central part of the sigmoid even though the twist of field lines is weak in this region. On the other hand, the highly twisted field lines with the weak X-ray emission occupy the outer region corresponding to elbow parts of sigmoid. The twist of these field lines is estimated as 0.75 < |Tn| < 1.5. This result is similar to the result obtained from a flux emergence simulation by Magara 2004. Magara 2004 showed that the weak twist occupies the central part of sigmoid. Our result supports a scenario that sigmoidal structure is formed by flux emergence.

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