Quasi-periodic pulsations in the most powerful solar flare of Cycle 24

TL;DR

This study identifies two types of quasi-periodic pulsations in the most powerful solar flare of Cycle 24, linking their properties to plasma oscillations and suggesting similar processes in solar and stellar flares.

Contribution

It provides the first detailed analysis of dual QPP signals in a major solar flare, connecting observed periods to specific plasma oscillation mechanisms.

Findings

Short-period QPP drifts from 12 to 25 seconds

Long-period QPP is about 4 to 5 minutes

Similar QPP mechanisms may operate in solar and stellar flares

Abstract

Quasi-periodic pulsations (QPP) are common in solar flares and are now regularly observed in stellar flares. We present the detection of two different types of QPP signals in the thermal emission light curves of the X9.3 class solar flare SOL2017-09-06T12:02, which is the most powerful flare of Cycle 24. The period of the shorter-period QPP drifts from about 12 to 25 seconds during the flare. The observed properties of this QPP are consistent with a sausage oscillation of a plasma loop in the flaring active region. The period of the longer-period QPP is about 4 to 5 minutes. Its properties are compatible with standing slow magnetoacoustic oscillations, which are often detected in coronal loops. For both QPP signals, other mechanisms such as repetitive reconnection cannot be ruled out, however. The studied solar flare has an energy in the realm of observed stellar flares, and the fact that there is evidence of a short-period QPP signal typical of solar flares along with a long-period QPP signal more typical of stellar flares suggests that the different ranges of QPP periods typically observed in solar and stellar flares is likely due to observational constraints, and that similar physical processes may be occurring in solar and stellar flares.