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Register a new userQuasi-Periodic Particle Acceleration in a Solar Flare
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A common feature of electromagnetic emission from solar flares is the presence of intensity pulsations that vary as a function of time. Known as quasi-periodic pulsations (QPPs), these variations in flux appear to include periodic components and characteristic time-scales. Here, we analyse a GOES M3.7 class flare exhibiting pronounced QPPs across a broad band of wavelengths using imaging and time-series analysis. We identify QPPs in the timeseries of X-ray, low frequency radio and EUV wavelengths using wavelet analysis, and localise the region of the flare site from which the QPPs originate via X-ray and EUV imaging. It was found that the pulsations within the 171 .A, 1600 .A, soft X-ray (SXR), and hard X-ray (HXR) light curves yielded similar periods of $sim$122 s, $sim$131s, $sim$123 s, and $sim$137 s, respectively, indicating a common progenitor. The low frequency radio emission at 2.5 MHz contained a longer period of $sim$231 s. Imaging analysis indicates that the location of the X-ray and EUV pulsations originates from a HXR footpoint linked to a system of nearby open magnetic field lines. Our results suggest that intermittent particle acceleration, likely due to bursty magnetic reconnection, is responsible for the QPPs. The precipitating electrons accelerated towards the chromosphere produce the X-ray and EUV pulsations, while the escaping electrons result in low frequency radio pulses in the form of type III radio bursts. The modulation of the reconnection process, resulting in episodic particle acceleration, explains the presence of these QPPs across the entire spatial range of flaring emission.
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Solar flares - the most powerful explosions in the solar system - are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well-reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares.
We explore the Quasi-Periodic Pulsations (QPPs) in a solar flare observed by Fermi Gamma-ray Burst Monitor (GBM), Solar Dynamics Observatory (SDO), Solar Terrestrial Relations Observatory (STEREO), and Interface Region Imaging Spectrograph (IRIS) on 2014 September 10. QPPs are identified as the regular and periodic peaks on the rapidly-varying components, which are the light curves after removing the slowly-varying components. The QPPs display only three peaks at the beginning on the hard X-ray (HXR) emissions, but ten peaks on the chromospheric and coronal line emissions, and more than seven peaks (each peak is corresponding to a type III burst on the dynamic spectra) at the radio emissions. An uniform quasi-period about 4 minutes are detected among them. AIA imaging observations exhibit that the 4-min QPPs originate from the flare ribbon, and tend to appear on the ribbon front. IRIS spectral observations show that each peak of the QPPs tends to a broad line width and a red Doppler velocity at C I, O IV, Si IV, and Fe XXI lines. Our findings indicate that the QPPs are produced by the non-thermal electrons which are accelerated by the induced quasi-periodic magnetic reconnections in this flare.
Solar flares often display pulsating and oscillatory signatures in the emission, known as quasi-periodic pulsations (QPP). QPP are typically identified during the impulsive phase of flares, yet in some cases, their presence is detected late into the decay phase. Here, we report extensive fine structure QPP that are detected throughout the large X8.2 flare from 2017 September 10. Following the analysis of the thermal pulsations observed in the GOES/XRS and the 131 A channel of SDO/AIA, we find a pulsation period of ~65 s during the impulsive phase followed by lower amplitude QPP with a period of ~150 s in the decay phase, up to three hours after the peak of the flare. We find that during the time of the impulsive QPP, the soft X-ray source observed with RHESSI rapidly rises at a velocity of approximately 17 km/s following the plasmoid/coronal mass ejection (CME) eruption. We interpret these QPP in terms of a manifestation of the reconnection dynamics in the eruptive event. During the long-duration decay phase lasting several hours, extended downward contractions of collapsing loops/plasmoids that reach the top of the flare arcade are observed in EUV. We note that the existence of persistent QPP into the decay phase of this flare are most likely related to these features. The QPP during this phase are discussed in terms of MHD wave modes triggered in the post-flaring loops.
We studied a solar flare with pronounced quasi-periodic pulsations detected in the microwave, X-ray, and radio bands. We used the methods of correlation, Fourier, and wavelet analyses to examine the temporal fine structures and relationships between the time profiles in each wave band. We found that the time profiles of the microwaves, hard X-rays and type III radio bursts vary quasi-periodically with the common period of 40-50 s. The average amplitude of the variations is high, above 30% of the background flux level and reaching 80% after the flare maximum. We did not find the periodicity in either the thermal X-ray flux component or source size dynamics. Our findings indicate that the detected periodicity is likely to be associated with periodic dynamics in the injection of non-thermal electrons, that can be produced by periodic modulation of magnetic reconnection.
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.
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