Non-damping oscillations at flaring loops

Abstract

Context. Quasi-periodic oscillations are usually detected as spatial displacements of coronal loops in imaging observations or as periodic shifts of line properties (i.e., Doppler velocity, line width and intensity) in spectroscopic observations. They are often applied for remote diagnostics of magnetic fields and plasma properties on the Sun. Aims. We combine imaging and spectroscopic measurements of available space missions, and investigate the properties of nondamping oscillations at flaring loops. Methods. We used the Interface Region Imaging Spectrograph (IRIS) to measure the spectrum over a narrow slit. The doublecomponent Gaussian fitting method was used to extract the line profile of Fe xxi 1354.08 Å at the 'O i' spectral window. The quasiperiodicity of loop oscillations were identified in the Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected in the line properties of Fe xxi 1354.08 Å, hard X-ray emissions in GOES 1−8 Å derivative, and Fermi 26−50 keV. The Doppler velocity and line width oscillate in phase, while a phase shift of about π/2 is detected between the Doppler velocity and peak intensity. The amplitudes of Doppler velocity and line width oscillation are about 2.2 km s −1 and 1.9 km s −1 , respectively, while peak intensity oscillate with amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period of about 155 s is identified in the Doppler velocity and peak intensity of the Fe xxi 1354.08 Å line emission, and AIA 131 Å intensity. Conclusions. The oscillations at about 40 s are not damped significantly during the observation, it might be linked to the global kink modes of flaring loops. The periodicity at about 155 s is most likely a signature of recurring downflows after chromospheric evaporation along flaring loops. The magnetic field strengths of the flaring loops are estimated to be about 120−170 G using the MHD seismology diagnostics, which are consistent with the magnetic field modeling results using the flux rope insertion method.

A Compact Source for Quasi-periodic Pulsation in an M-class Solar Flare

“…If we consider the periodicity at MHD timescale and its persistence, such a signal resembles the leakage of sunspot oscillations Li et al 2018). However, we did not observe similar oscillatory signal propagating along the loops in the EUV emission intensity (see Figure 4a), so we rule out the possibility of leakage of sunspot oscillation in forms of slow mode wave.…”

Motion Magnification in Solar Imaging Data Sequences in the Sub-pixel Regime

“…Oscillations of this type have first been observed by Wang et al (2012) with the imaging EUV telescope Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO: Lemen et al, 2012). Similar oscillations are detected as persistent Doppler-shift oscillations at loop apexes (Tian et al, 2012;Li et al, 2018). Anfinogentov, Nisticò, and Nakariakov (2013) demonstrated the ubiquity of decayless kink oscillations of coronal loops, which opens up interesting perspectives for regular seismological probing of the magnetic field in coronal active regions (Anfinogentov and Nakariakov, 2019).…”

Doppler shift oscillations of a sunspot detected by CYRA and IRIS

“…It can be seen that the trend velocity is close to zero. Panel b displays the detrended velocity after subtracting the four-minute running average (e.g., Wang et al 2009;Li et al 2018), which exhibits five pronounced peaks within a duration of 25 minutes, suggesting a 5 min periodicity. The 5 min periodicity is confirmed by the wavelet power spectrum shown in panel c. It clearly shows a period of 5 min above the confidence level of 99% (red contour).…”