NuSTAR Observation of Energy Release in 11 Solar Microflares

Duncan, Jessie; Glesener, Lindsay; Grefenstette, Brian W.; Vievering, Juliana; Hannah, I. G.; Smith, David M.; Krucker, S.; White, S. M.; Hudson, H. S.

doi:10.3847/1538-4357/abca3d

Cited by 26 publications

(32 citation statements)

References 38 publications

(64 reference statements)

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“…Observations of such small events are possible due to NuSTAR's sensitivity during the solar minimum between cycle 24 and 25. Non-thermal emission has also been directly observed with NuSTAR's focusing optics imaging spectroscopy in a GOES class A5.7 microflare (Glesener et al 2020) with other studies finding a non-thermal power source consistent with the microflares under investigation (Wright et al 2017;Cooper et al 2020;Duncan et al 2021). 1 In this paper we present observations of all identified microflares observed by NuSTAR from AR12721 on 2018 September 9-10.…”

Section: Introductionsupporting

confidence: 66%

“…Therefore, most of the hotter material in these data is likely constrained below 10 MK. Therefore, the Fe synthetic channel is an appropriate candidate to corroborate the hotter thermally emitting material that NuSTAR observes from microflares (Hannah et al 2016;Wright et al 2017;Hannah et al 2019;Glesener et al 2020;Duncan et al 2021).…”

Section: Nustar Observations: 2018 September 9-10mentioning

confidence: 99%

“…NuSTAR has observed several B, A, and equivalent sub-A class AR microflares of energies from 10 28 erg down to 10 26 erg (Glesener et al 2017;Wright et al 2017;Hannah et al 2019;Cooper et al 2020;Duncan et al 2021). Quiet Sun brightenings outside ARs have also been observed with thermal energies of 10 26 erg (Kuhar et al 2018).…”

Section: Introductionmentioning

confidence: 96%

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NuSTAR observations of a repeatedly microflaring active region

Cooper,

Hannah,

Grefenstette

et al. 2021

Preprint

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We investigate the spatial, temporal, and spectral properties of 10 microflares from AR12721 on 2018 September 9 and 10 observed in X-rays using the Nuclear Spectroscopic Telescope ARray (NuSTAR) and the Solar Dynamic Observatory's Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager (SDO/AIA and HMI). We find GOES sub-A class equivalent microflare energies of 10 26 -10 28 erg reaching temperatures up to 10 MK with consistent quiescent or hot active region core plasma temperatures of 3-4 MK. One microflare (SOL2018-09-09T10:33), with an equivalent GOES class of A0.1, has nonthermal HXR emission during its impulsive phase (of non-thermal power ∼7×10 24 erg s −1 ) making it one of the faintest X-ray microflares to have direct evidence for accelerated electrons. In 4 of the 10 microflares, we find that the X-ray time profile matches fainter and more transient sources in the EUV, highlighting the need for observations sensitive to only the hottest material that reaches temperatures higher than those of the active region core (>5 MK). Evidence for corresponding photospheric magnetic flux cancellation/emergence present at the footpoints of 8 microflares is also observed.

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Section: Introductionsupporting

confidence: 66%

Section: Nustar Observations: 2018 September 9-10mentioning

confidence: 99%

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NuSTAR observations of a repeatedly microflaring active region

Cooper,

Hannah,

Grefenstette

et al. 2021

Preprint

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“…As detailed observations have been lacking, it is not clear if the evolution of these smaller events follows the standard flare model. It is only recently, with the advent of better instrumentation, that in-depth studies of smaller flares are becoming feasible (Kuhar et al 2018;Mitra-Kraev and Del Zanna 2019;Athiray et al 2020;Cooper et al 2020;Glesener et al 2020;Duncan et al 2021;Vadawale et al 2021a). Lately, using X-ray time resolved spectroscopy, Narendranath et al (2020) have carried out abundance studies of flares as small as GOES B9-class.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Elemental Abundances During B-Class Solar Flares: Soft X-ray Spectral Measurements with Chandrayaan-2 XSM

Mondal,

Sarkar,

Vadawale

et al. 2021

Preprint

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The Solar X-ray Spectrometer (XSM) payload onboard Chandrayaan-2 provides disk-integrated solar spectra in the 1 -15 keV energy range with an energy resolution of 180 eV (at 5.9 keV) and a cadence of 1 second. During the period from September 2019 to May 2020, covering the minimum of Solar Cycle 24, it observed nine B-class flares ranging from B1.3 to B4.5. Using time-resolved spectroscopic analysis during these flares, we examined the evolution of temperature, emission measure, and absolute elemental abundances of four elements -Mg, Al, Si, and S. These are the first measurements of absolute abundances during such small flares and this study offers a unique insight into the evolution of absolute abundances as the flares evolve. Our results demonstrate that the abundances of these four elements decrease towards their photospheric values during the peak phase of the flares. During the decay phase, the abundances are observed to quickly return to their pre-flare coronal values. The depletion of elemental abundances during the flares is consistent with the standard flare model, suggesting the injection of fresh material into coronal loops as a result of chromospheric evaporation. To explain the quick recovery of the so-called coronal "First Ionization Potential (FIP) bias" we propose two scenarios based on the Ponderomotive force model.

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“…However, even smaller flares, so-called microflares (Hannah et al 2011) can display a remarkable complexity as demonstrated by e.g. Sharma et al (2020), Glesener et al (2020), Duncan et al (2021), andVievering et al (2021). Understanding this complexity and different features observed at both, radio and X-ray wavelengths, is the key to understanding where and how electron acceleration takes place and how electrons are transported.…”

Section: Introductionmentioning

confidence: 99%

Multiple electron acceleration instances during a series of solar microflares observed simultaneously at X-rays and microwaves

Battaglia,

Sharma,

Luo

et al. 2021

Preprint

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Even small solar flares can display a surprising level of complexity regarding their morphology and temporal evolution. Many of their properties, such as energy release and electron acceleration can be studied using highly complementary observations at X-ray and radio wavelengths. We present X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and radio observations from the Karl G. Jansky Very Large Array (VLA) of a series of GOES A3.4 to B1.6 class flares observed on 2013 April 23. The flares, as seen in X-ray and extreme ultraviolet (EUV), originated from multiple locations within active region NOAA 11726. A veritable zoo of different radio emissions between 1 GHz and 2 GHz was observed co-temporally with the X-ray flares. In addition to broad-band continuum emission, broad-band short-lived bursts and narrow-band spikes, indicative of accelerated electrons, were observed. However, these sources were located up to 150 arcsec away from the flaring X-ray sources but only some of these emissions could be explained as signatures of electrons that were accelerated near the main flare site. For other sources, no obvious magnetic connection to the main flare site could be found. These emissions likely originate from secondary acceleration sites triggered by the flare, but may be due to reconnection and acceleration completely unrelated to the co-temporally observed flare. Thanks to the extremely high sensitivity of the VLA, not achieved with current X-ray instrumentation, it is shown that particle acceleration happens frequently and at multiple locations within a flaring active region.

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NuSTAR Observation of Energy Release in 11 Solar Microflares

Cited by 26 publications

References 38 publications

NuSTAR observations of a repeatedly microflaring active region

NuSTAR observations of a repeatedly microflaring active region

Evolution of Elemental Abundances During B-Class Solar Flares: Soft X-ray Spectral Measurements with Chandrayaan-2 XSM

Multiple electron acceleration instances during a series of solar microflares observed simultaneously at X-rays and microwaves

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