31 research outputs found
An ultra-long and quite thin coronal loop without significant expansion
Context. Coronal loops are the basic building blocks of the solar corona,
which are related to the mass supply and heating of solar plasmas in the
corona. However, their fundamental magnetic structures are still not well
understood. Most coronal loops do not expand significantly, whereas the
diverging magnetic field would have an expansion factor of about 5-10 over one
pressure scale height. Aims. In this study, we investigate a unique coronal
loop with a roughly constant cross section, it is ultra long and quite thin. A
coronal loop model with magnetic helicity is presented to explain the small
expansion of the loop width. Methods. This coronal loop was predominantly
detectable in the 171 A channel of the Atmospheric Imaging Assembly (AIA).
Then, the local magnetic field line was extrapolated by a
Potential-Field-Source-Surface model. Finally, the differential emission
measure analysis made from six AIA bandpasses was applied to obtain the thermal
properties of this loop. Results. This coronal loop has a projected length of
roughly 130 Mm, a width of about 1.5 +(-) 0.5 Mm and a lifetime of around 90
minutes. It follows an open magnetic field line. The cross section expanded
very little (i.e., 1.5-2.0) along the loop length during its whole lifetime.
This loop has a nearly constant temperature at about 0.7 +(-) 0.2 MK, whereas
its density exhibits the typical structure of a stratified atmosphere.
Conclusions. We use a thin twisted flux tube theory to construct a model for
this non-expanding loop, and find that indeed with sufficient twist a coronal
loop can attain equilibrium. However, we can not rule out other possibilities
such as footpoint heating by small-scale reconnection, elevated scale height by
a steady flow along the loop etc.Comment: 8 pages, 5 figures, 1 table
Simultaneous detection of flare-associated kink oscillations and extreme-ultraviolet waves
Kink oscillations, which are frequently observed in coronal loops and
prominences, are often accompanied by extreme-ultraviolet (EUV) waves. However,
much more needs to be explored regarding the causal relationships between kink
oscillations and EUV waves. In this article, we report the simultaneous
detection of kink oscillations and EUV waves that are both associated with an
X2.1 flare on 2023 March 03 (SOL2023-03-03T17:39). The kink oscillations, which
are almost perpendicular to the axes of loop-like structures, are observed in
three coronal loops and one prominence. One short loop shows in-phase
oscillation within the same period of 5.2 minutes at three positions. This
oscillation could be triggered by the pushing of an expanding loop and
interpreted as the standing kink wave. Time lags are found between the kink
oscillations of the short loop and two long loops, suggesting that the kink
wave travels in different loops. The kink oscillations of one long loop and the
prominence are possibly driven by the disturbance of the CME, and that of
another long loop might be attributed to the interaction of the EUV wave. The
onset time of the kink oscillation of the short loop is nearly same as the
beginning of an EUV wave. This fact demonstrates that they are almost
simultaneous. The EUV wave is most likely excited by the expanding loop
structure and shows two components. The leading component is a fast coronal
wave, and the trailing one could be due to the stretching magnetic field lines.Comment: accepted for publication in the Science China Technological Science