Evolution of a Coronal Twisted Flux Rope

arXiv:0902.0589v1 [astro-ph.SR] 3 Feb 2009 Second Hinode Science Meeting ASP Conference Series, Vol. xxx, 2009 M. Cheung, B. Lites, T. Magara, J. Mariska, and K. Reeves Evolution of a Coronal Twisted Flux Rope Nour-Eddine Raouafi Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA. e-mail: Nour.Eddine.Raouafi@jhuapl.edu Abstract. Multi-instrument observations of NOAA AR10938 on Jan. 14- 18, 2007, are utilized to study the evolution of a magnetic thread system with multiple crossings suggestive of a twisted coronal flux rope. A C-class flare recorded by GOES on Jan. 16, at approximately 2:35 UT led to the brightening of the structure, that is seen in Hinode/EIS data at 2:46 UT, Hinode/XRT after 2:50 UT, and STEREO/SECCHI/EUVI images at 3:30 UT. 304 ˚A images revealed the presence of rapidly evolving, dark fibrils along the bright structure before and after the flare. A denser structure formed a few hours later and lasted for several days forming a segment of an inverse S-shaped filament. The present set of data is highly suggestive of the presence of a twisted flux rope prior to the formation of the filament segment at the same location. 1. Introduction Multi-wavelength observations show that most solar eruptive events (flares and coronal mass ejections: CMEs) are associated with magnetic fields with complex topologies (twist, shear, writhe, and linking; see Canfield et al. 1999). Hence, numerous recent studies were dedicated to characterize the formation of solar filaments and their eruptive evolution into CMEs. Resolving the magnetic struc- ture of these phenomena is therefore important to constrain models (see Chae 2000). We use multi-instrument observations of NOAA AR10938 on Jan. 14-18, 2007, to study the evolution of a magnetic thread system with multiple crossing that is highly suggestive of a flux rope. 2. Observations and Data Analysis Raouafi(2009) reported on a non-eruptive C-class flare recorded by GOES in AR10938 on Jan. 16, 2007, at approximately 2:35 UT, which led to the brighten- ing of the complex magnetic thread system. Data from the Hinode X-Ray tele- scope (XRT: Golub et al. 2007), the Extreme UV Imaging Spectrometer (EIS: Culhane et al. 2007) and the Solar Optical Telescope (SOT: Tsuneta et al. 2008) filtergram are used to study the formation and evolution of the structure along with EUV images from STEREO/SECCHI/EUVI (EUVI: Howard et al. 2008). The different data sets provide a temperature coverage ranging from ∼0.08 MK to > 10 MK. This is important to study the temporal evolution of the structure. Fig. 1 displays a LOS-photospheric magnetogram from SOT-FG of the ac- tive region. The magnetic structure extends between the triangle symbols that mark approximately the locations of its footpoints. The loop-system ends are rooted into pores and plage areas with opposite dominant polarities, where rel- atively important changes of the flux were occurring (see right panel of Fig. 1). 1 2 Nour-Eddine Raouafi2009 Figure 1. Left: LOS-magnetogram from Hinode/SOT-FG. The triangles indicate approximately the footpoint locations of the magnetic loop system. Right: difference of the unsigned magnetic flux. The GOES non-eruptive, C-class flare took place near the northeast footpoint (see Fig. 2a). Figure 2. NOAA AR10938 as seen by Hinode/XRT prior to and after the flare. The magnetic thread system is best seen around 3:00 UT. The individual threads indicate a multiple crossing topology highly suggestive of a flux rope. The full extend of the magnetic thread system is revealed by emissions of high temperature spectral lines observed by EIS (Fe xxiv 255.1 ˚A: log T = 7.2; Ca xvii 192.82 ˚A: log T = 6.7) at about 2:46 UT. The loop topology in EIS data is similar to the X-Ray one recorded about 15-20 minutes after the flare (Fig. 2) with, however, a better contrast. It is noteworthy that emissions in low temperature lines did not show similar features. X-Ray data also show that the structure had an apparent simpler topology prior to the flare. EUVI-A observations in the 171 ˚A and 195 ˚A channels show the relatively cool (∼1 MK) counterpart of the loop system observed earlier by EIS and XRT. Fig. 3 displays snapshots of AR10938 recorded between 3:00 UT and 4:00 UT. Evolution of a Coronal Twisted Flux Rope 3 Figure 3. 195 ˚A images from EUVI-A on Jan. 16, 2007, illustrating the evo- lution of the EUV counterpart of the X-ray threads observed by Hinode/XRT. The EUV structure looks similar to that observed in X-rays with, however, a time gap greater than 30 minutes in appearance. The EUVI structure is very similar to the one observed earlier in EIS’s hot lines with, however, a delay greater than 45 minutes. The arrangement of the threads is better seen around 3:30 UT and show similarities with EIS and XRT observations. The sequential appearances of the suggested flux rope in hot emission lines (e.g., Fe xxiv 225.1 ˚A, log T = 7.2), then in X-ray images (a few MK), and finally in EUV 171 ˚A and 195 ˚A images (∼1 MK) sh

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