Microwave imaging of quasi-periodic pulsations at flare current sheet

Kou, Yuankun; Cheng, X.; Wang, Yulei; Yu, Sijie; Bin, Chen; Kontar, Eduard P.; Ding, M. D.

doi:10.1038/s41467-022-35377-0

Cited by 15 publications

(15 citation statements)

References 68 publications

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“…There are multiple pathways for the reconnection to be periodic, either due to an inherent energy release timescale, including tearing mode or other instability, or a periodic external forcing. Periodic reconnection in the solar corona occurs during flares, resulting in Quasi‐periodic pulsations (QPPs) (Kou et al., 2022; Nakariakov & Melnikov, 2009). QPPs are regularly observed in other stars, for example, using XMM‐Newton (Cho et al., 2016) and GALEX (Doyle et al., 2018; Welsh et al., 2006), pointing to the universality of periodic magnetic reconnection in solar and stellar atmospheres.…”

Section: Discussionmentioning

confidence: 99%

Periodic Mesoscale Density Structures Comprise a Significant Fraction of the Solar Wind and Are Formed at the Sun

Kepko,

Viall,

DiMatteo

2024

JGR Space Physics

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Mesoscale density structures in the solar wind are often periodic, with f ∼ 0.1–5 mHz. They are trains of advected density structures with radial length scales of ∼100–10,000 Mm. While studies have shown that these periodic density structures (PDSs) are often formed at the Sun and released into the solar wind, it is unknown what percent of the solar wind at 1 AU is comprised of PDSs from the Sun, as opposed to periodicities formed through dynamics en route. We expand on Kepko et al. (2020, https://doi.org/10.1029/2020ja028037) which analyzed 25 years of in situ solar wind proton data, and include here alphas to examine the compositional characteristics of PDSs. Compositional changes, such as the alpha‐to‐proton ratio (α/p), are frozen into the solar wind plasma low in the corona, and so do not evolve as the solar wind advects and fills the Heliosphere. We find a broad occurrence enhancement in both the proton and α/p distributions between 1 and 3 mHz, centered near ∼2.1 mHz, and demonstrate that this distribution can be modeled assuming ∼30% of the solar wind segments contain a PDS. We find a distinct distribution below 1 mHz, with markedly different α/p characteristics. The α/p indicates that both populations are from the Sun, with likely different generation mechanisms. We conclude by summarizing mechanisms at the Sun that could produce periodic mass release, namely, periodic magnetic reconnection. The lower frequency PDSs likely involve reconnection at S‐web arcs including the heliospheric current sheet, while the higher frequency PDSs may be driven by p‐mode‐related transverse coronal oscillations.

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Section: Discussionmentioning

confidence: 99%

Periodic Mesoscale Density Structures Comprise a Significant Fraction of the Solar Wind and Are Formed at the Sun

Kepko,

Viall,

DiMatteo

2024

JGR Space Physics

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“…Almost at the same time, EOVSA went back to the Sun at 19:31 UT and fully covered the post-impulsive phase. In this phase, three broadband bursts can be observed in the EOVSA 1-18 GHz dynamic spectrum (Figure 2 integrated from 19:32 UT to 19:45 UT with 134 frequencies in 2.5-18 GHz over 31 evenly spaced spectral windows (referred to as SPW 0 to SPW 30) and is conducted with a temporal resolution of 10 s. While post-impulsive phase microwave bursts have been reported in the literature (e.g., Yu et al 2020;Kou et al 2022), this event shows an increase in the peak intensity of bursts that occur later. The peak flux density at 9.4 GHz, for example, increases from 50 sfu for the first burst to 114 sfu for the last one.…”

Section: Microwave and X-ray Bursts During The Main And Postimpulsive...mentioning

confidence: 91%

Episodic Energy Release during the Main and Post-impulsive Phases of a Solar Flare

Wei,

Chen 陈,

Yu 余

et al. 2024

ApJ

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When and where the magnetic field energy is released and converted in eruptive solar flares remains an outstanding topic in solar physics. To shed light on this question, here we report multiwavelength observations of a C9.4-class eruptive limb flare that occurred on 2017 August 20. The flare, accompanied by a magnetic flux rope eruption and a white light coronal mass ejection, features three post-impulsive X-ray and microwave bursts immediately following its main impulsive phase. For each burst, both microwave and X-ray imaging suggest that the nonthermal electrons are located in the above-the-loop-top region. Interestingly, contrary to many other flares, the peak flux of the three post-impulsive microwave and X-ray bursts shows an increase for later bursts. Spectral analysis reveals that the sources have a hardening spectral index, suggesting a more efficient electron acceleration into the later post-impulsive bursts. We observe a positive correlation between the acceleration of the magnetic flux rope and the nonthermal energy release during the post-impulsive bursts in the same event. Intriguingly, different from some other eruptive events, this correlation does not hold for the main impulse phase of this event, which we interpret as energy release due to the tether-cutting reconnection before the primary flux rope acceleration occurs. In addition, using footpoint brightenings at conjugate flare ribbons, a weakening reconnection guide field is inferred, which may also contribute to the hardening of the nonthermal electrons during the post-impulsive phase.

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“…In this paper we use the Wavelet Transform analysis developed by Torrence & Compo (1998) and modified by Auchère et al (2016). This method has been applied to detect QPPs in solar (Clarke et al 2021;Kou et al 2022)…”

Section: Quantifying Quasiperiodic Pulsationsmentioning

confidence: 99%

Inferring Fundamental Properties of the Flare Current Sheet Using Flare Ribbons: Oscillations in the Reconnection Flux Rates

Corchado Albelo,

Kazachenko,

Lynch

2024

ApJ

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Magnetic reconnection is understood to be the main physical process that facilitates the transformation of magnetic energy into heat, motion, and particle acceleration during solar eruptions. Yet, observational constraints on reconnection region properties and dynamics are limited due to a lack of high-cadence and high-spatial-resolution observations. By studying the evolution and morphology of postreconnected field-lines footpoints, or flare ribbons and vector photospheric magnetic field, we estimate the magnetic reconnection flux and its rate of change with time to study the flare reconnection process and dynamics of the current sheet above. We compare high-resolution imaging data to study the evolution of the fine structure in flare ribbons as ribbons spread away from the polarity inversion line. Using data from two illustrative events (one M- and X-class flare), we explore the relationship between the ribbon-front fine structure and the temporal development of bursts in the reconnection region. Additionally, we use the RibbonDB database to perform statistical analysis of 73 (C- to X-class) flares and identify quasiperiodic pulsation (QPP) properties using the Wavelet Transform. Our main finding is the discovery of QPP signatures in the derived magnetic reconnection rates in both example events and the large flare sample. We find that the oscillation periods range from 1 to 4 minutes. Furthermore, we find nearly cotemporal bursts in Hard X-ray (HXR) emission profiles. We discuss how dynamical processes in the current sheet involving plasmoids can explain the nearly cotemporal signatures of quasiperiodicity in the reconnection rates and HXR emission.

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Microwave imaging of quasi-periodic pulsations at flare current sheet

Cited by 15 publications

References 68 publications

Periodic Mesoscale Density Structures Comprise a Significant Fraction of the Solar Wind and Are Formed at the Sun

Periodic Mesoscale Density Structures Comprise a Significant Fraction of the Solar Wind and Are Formed at the Sun

Episodic Energy Release during the Main and Post-impulsive Phases of a Solar Flare

Inferring Fundamental Properties of the Flare Current Sheet Using Flare Ribbons: Oscillations in the Reconnection Flux Rates

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