Detection and Interpretation of Long-lived X-Ray Quasi-periodic Pulsations in the X-class Solar Flare on 2013 May 14

Abstract

Quasi-periodic pulsations (QPP) seen in the time derivative of the GOES soft X-ray light curves are analyzed for the near-limb X3.2 event on 14 May 2013. The pulsations are apparent for a total of at least two hours from the impulsive phase to well into the decay phase, with a total of 163 distinct pulses evident to the naked eye. A wavelet analysis shows that the characteristic time scale of these pulsations increases systematically from ∼25 s at 01:10 UT, the time of the GOES peak, to ∼100 s at 02:00 UT. A second 'ridge' in the wavelet power spectrum, most likely associated with flaring emission from a different active region, shows an increase from ∼40 s at 01:40 UT to ∼100 s at 03:10 UT. We assume that the QPP that produced the first ridge result from vertical kink-mode oscillations of the newly formed loops following magnetic reconnection in the coronal current sheet. This allows us to estimate the magnetic field strength as a function of altitude given the density, loop length, and QPP time scale as functions of time determined from the GOES light curves and RHESSI images. The calculated magnetic field strength of the newly formed loops ranges from ∼500 G at an altitude of 24 Mm to a low value of ∼10 G at 60 Mm, in general agreement with the expected values at these altitudes. Fast sausage mode oscillations are also discussed and cannot be ruled out as an alternate mechanism for producing the QPP.

Properties of quasi-periodic pulsations in solar flares from a single active region

“…Kupriyanova et al 2010) and hence would not have a well defined peak in the power spectrum, the QPPs could be too low amplitude or have the wrong period to be detectable with the instruments operating at the time, or lower quality QPP signals could have been missed during the manual search stage. Additionally we show how taking the time derivative of light curve data, which has previously been shown to be useful when searching for QPPs (Simões et al 2015;Hayes et al 2016;Dennis et al 2017), impacts the power spectrum, and suggest how this can be accounted for when searching for periodic signals. Out of the 44 flares in this sample that overlap with those included by Inglis et al (2016), we find the same periods in 6 (or 13 if the selection criteria used by Inglis et al (2016) are relaxed) and agree with the lack of evidence of a QPP signal in a further 24.…”

“…Making use of the time derivative of high-precision SXR observations has been shown to be useful for the study of QPPs (Simões et al 2015;Hayes et al 2016;Dennis et al 2017). Taking the derivative will have a significant impact on the power spectrum of time series data, however, and so it is extremely important to understand this impact when assessing the significance of peaks in the power spectrum.…”

Quasi-periodic Pulsations in the Most Powerful Solar Flare of Cycle 24

“…As shown by previous studies, QPP can be more easily detected in the time derivative of soft X-ray (SXR) observations than in the raw observations themselves (e.g. Simões et al 2015;Hayes et al 2016;Dennis et al 2017). This is because the change in SXR flux during the impulsive phase of a flare, where QPP are predominantly observed, is often vastly greater in amplitude than the QPP being searched for.…”

Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares

“…The recently detected very long period pulsations of the plasma temperature before the onset of flares (8-30 min "preflare-VLPs", Tan et al 2016) may perhaps be linked to this effect too. In addition, this effect may be responsible for the high-quality oscillatory patterns of the thermal X-ray emission, with the intermittent variation of the amplitude, detected in the time derivative of the GOES light curves of X-class flares by Simões et al (2015) (see also Dennis et al 2017). …”