Comparison of Damped Oscillations in Solar and Stellar X-Ray Flares

Abstract

We explore the similarity and difference of the quasi-periodic pulsations (QPPs) observed in the decay phase of solar and stellar flares at X-rays. We identified 42 solar flares with pronounced QPPs, observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and 36 stellar flares with QPPs, observed with X-ray Multi Mirror Newton observatory (XMM-Newton). The Empirical Mode Decomposition (EMD) method and least-square fit by a damped sine function were applied to obtain the periods (P ) and damping times (τ ) of the QPPs. We found that (1) the periods and damping times of the stellar QPPs are 16.21±15.86 min and 27.21±28.73 min, while those of the solar QPPs are 0.90±0.56 and 1.53±1.10 min, respectively. (2) The ratio of the damping times to the periods (τ /P ) observed in the stellar QPPs (1.69±0.56) are statistically identical to those of solar QPPs (1.74±0.77). (3) The scalings of the QPP damping time with the period are well described by the power law in both solar and stellar cases. The power indices of the solar and stellar QPPs are 0.96±0.10 and 0.98±0.05, respectively. This scaling is consistent with the scalings found for standing slow magnetoacoustic and kink modes in solar coronal loops. Thus, we propose that the underlying mechanism responsible for the stellar QPPs is the natural magnetohydrodynamic oscillations in the flaring or adjacent coronal loops, as in the case of solar flares.

Non-stationary quasi-periodic pulsations in solar and stellar flares

“…This result is unexpected, as the dissipative mechanisms that affect coronal magnetoacoustic waves: thermal conduction, viscosity and resistivity, should lead to the quadratic dependence. Intriguingly, this unusual linear scaling has been found in soft x-ray QPP in both solar and stellar flares [31], as well as in the SUMER oscillations directly observed in the Doppler shift, and hence is a robust empirical result. Usually, the damping time is determined from the best-fitting exponential decay function.…”

“…Operating locally and hence adaptively, it iteratively sifts these time scales from the signal thus forming a set of intrinsic mode functions (IMFs or 'intrinsic modes') each of them potentially representing a certain non-stationary and anharmonic oscillatory process in the original signal. EMD has been used for the detection of non-stationary multi-modal QPP in solar (e.g., [28,31,32]) and stellar flares (e.g., [31,33]). However, the full scale application of this technique requires deeper understanding of its properties and shortcomings.…”

Stellar flare oscillations: evidence for oscillatory reconnection and evolution of MHD modes

“…More specifically, some QPPs exhibit periodic and decaying variation of the flux in a particular waveband after the flare peak, while others are only present in the impulsive phase. For solar flares, these range from milliseconds to a few minutes, while stellar flares can have oscillations of up to several tens of minutes (Welsh et al 2006;Simões, Hudson & Fletcher 2015;Cho et al 2016). If QPPs are generated by quasi-periodic processes, then this provides information on the ongoing physical processes during the flare, e.g.…”

“…They measured the density scale height of its corona to be smaller than the typical hydrostatic scale height, and indicated the presence of non-equilibrium conditions there. Cho et al (2016) looked at QPPs in solar flares with RHESSI and stellar flares using XMM data. Typical periods derived from stellar flares are 16.2 ± 15.9 min with a damping time of 27.1 ± 28.7 min, while for solar flares the QPPs period was 0.9 ± 0.6 min with a damping time of 1.5 ± 1.1 min.…”

Observation of a Short Period Quasi-periodic Pulsation in Solar X-Ray, Microwave, and EUV Emissions

“…Nakariakov & Melnikov 2009;Pandey & Srivastava 2009;Kupriyanova et al 2010;Simões et al 2015;Pugh et al 2015;Inglis et al 2015;Cho et al 2016). The physical mechanism for the generation of QPPs is important for understanding the drivers of the flaring energy releases, particle acceleration, associated plasma heating, and may be useful for the flare forecasting.…”