NONLINEAR FORCE-FREE MODELING OF A LONG-LASTING CORONAL SIGMOID

Journal Article · Thu Oct 01 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/2/1766· OSTI ID:21371879

Savcheva, Antonia

A study of the magnetic configuration and evolution of a long-lasting quiescent coronal sigmoid is presented. The sigmoid was observed by Hinode/XRT and Transition Region and Coronal Explorer (TRACE) between 2007 February 6 and 12 when it finally erupted. We construct nonlinear force-free field models for several observations during this period, using the flux-rope insertion method. The high spatial and temporal resolution of the X-Ray Telescope (XRT) allows us to finely select best-fit models that match the observations. The modeling shows that a highly sheared field, consisting of a weakly twisted flux rope embedded in a potential field, very well describes the structure of the X-ray sigmoid. The flux rope reaches a stable equilibrium, but its axial flux is close to the stability limit of about 5 x 10{sup 20} Mx. The relative magnetic helicity increases with time from February 8 until just prior to the eruption on February 12. We study the spatial distribution of the torsion parameter alpha in the vicinity of the flux rope, and find that it has a hollow-core distribution, i.e., electric currents are concentrated in a current layer at the boundary between the flux rope and its surroundings. The current layer is located near the bald patch separatrix surface (BPSS) of the magnetic configuration, and the X-ray emission appears to come from this current layer/BPSS, consistent with the Titov and Demoulin model. We find that the twist angle PHI of the magnetic field increases with time to about 2pi just prior to the eruption, but never reaches the value necessary for the kink instability.

• OSTI ID: 21371879
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 703; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CURRENTS
DISTRIBUTION
ELECTRIC CURRENTS
ELECTROMAGNETIC RADIATION
EMISSION
ERUPTION
GAMMA RADIATION
HELICITY
INSTABILITY
IONIZING RADIATIONS
KINK INSTABILITY
MAGNETIC FIELDS
MAIN SEQUENCE STARS
NONLINEAR PROBLEMS
PARTICLE PROPERTIES
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
RADIATIONS
RESOLUTION
SPATIAL DISTRIBUTION
STARS
SUN
TELESCOPES
X RADIATION