Oscillations in the Flaring Active Region NOAA 11272

Abstract

We studied waves seen during the class C1.9 flare that occurred in Active Region NOAA 11272 on SOL2011-08-17. We found standing waves with periods in the 9- and 19-minute band in six extreme ultraviolet (EUV) wavelengths of the SDO/AIA instrument. We succeeded in identifying the magnetic arc where the flare started and two neighbour loops that were disturbed in sequence. The analysed standing waves spatially coincide with these observed EUV loops. To study the wave characteristics along the loops, we extrapolated field lines from the line-of-sight magnetograms using the force-free approximation in the linear regime. We used atmosphere models to determine the mass density and temperature at each height of the loop. Then, we calculated the sound and Alfv{\'e}n speeds using densities $10^8 \lesssim n_i \lesssim 10^{17}$ cm$^{-3}$ and temperatures $10^3 \lesssim T \lesssim 10^7$ K. The brightness asymmetry in the observed standing waves resembles the Alfv{\'e}n speed distribution along the loops, but the atmospheric model we used needs higher densities to explain the observed periods.