NuSTAR observations of a repeatedly microflaring active region

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

doi:10.1093/mnras/stab2283

Cited by 23 publications

(21 citation statements)

References 60 publications

(85 reference statements)

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“…As a result, the SDO/AIA 211 Å lightcurves for these features sometimes do not show behaviour consistent with Hinode/XRT or with NuSTAR. Previous analysis of microflares observed with NuSTAR (for example, Cooper et al (2020Cooper et al ( , 2021) has made use of the SDO/AIA Fe XVIII proxy channel (Del Zanna, 2013). Unfortunately, the temperatures of these quiet Sun features are too low for this to be useful.…”

Section: Discussionmentioning

confidence: 99%

“…Since 2014, there have been a number of NuSTAR solar observing campaigns 1 . Much of the work on the NuSTAR solar observations has focused on active region microflares (Wright et al, 2017;Glesener et al, 2017;Hannah et al, 2019;Cooper et al, 2020;Duncan et al, 2021;Cooper et al, 2021), with Glesener et al (2020) reporting for the first time on non-thermal emission detected in a microflare observed with NuSTAR. Kuhar et al (2017) presented work on quiet Sun flares observed by NuSTAR outside of an active region, finding that their temperatures ranged from 3.2-4.1 MK.…”

Section: Introductionmentioning

confidence: 99%

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The First Survey of Quiet Sun Features Observed in Hard X-Rays With NuSTAR

Paterson¹,

Hannah²,

Grefenstette³

et al. 2022

Preprint

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We present the first survey of quiet Sun features observed in hard Xrays (HXRs), using the the Nuclear Spectroscopic Telescope ARray (NuSTAR), a HXR focusing optics telescope. The recent solar minimum combined with NuSTAR's high sensitivity has presented a unique opportunity to perform the first HXR imaging spectroscopy on a range of features in the quiet Sun. By studying the HXR emission of these features we can detect or constrain the presence of high temperature (>5 MK) or non-thermal sources, to help understand how they relate to larger more energetic solar phenomena, and determine their contribution to heating the solar atmosphere. We report on several features observed in the

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The First Survey of Quiet Sun Features Observed in Hard X-Rays With NuSTAR

Paterson¹,

Hannah²,

Grefenstette³

et al. 2022

Preprint

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“…A large spectral index (δ = 7) was chosen for the energy distribution, supported by observational evidence of increasing spectral index with decreasing flare energy (Hannah et al 2011), and compatible with values from rare hard X-ray observations of these small heating events (e.g., Glesener et al 2020;Cooper et al 2021). The low-energy cutoff values E C = 5, 10, and 15 keV were chosen to represent beams that are dominated by low-, intermediate-, and high-energy electrons.…”

Section: Parameter Surveymentioning

confidence: 99%

“…Signatures of non-thermal electrons are found in spectra from hard X-ray observations of active region flares. However, X-ray observations of small-scale events with energies in the range 10 24 -10 25 erg remain rare because signatures from non-thermal electrons are typically below the detection threshold (although, see e.g., Wright et al 2017;Glesener et al 2020;Cooper et al 2021). Indications of energetic events are obtained in regions that are responsive to heating.…”

Section: Introductionmentioning

confidence: 99%

Chromospheric emission from nanoflare heating in RADYN simulations

Bakke

Carlsson

Voort

et al. 2022

A&A

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Context. Heating signatures from small-scale magnetic reconnection events in the solar atmosphere have proven to be difficult to detect through observations. Numerical models that reproduce flaring conditions are essential in understanding how nanoflares may act as a heating mechanism of the corona. Aims. We study the effects of non-thermal electrons in synthetic spectra from 1D hydrodynamic RADYN simulations of nanoflare heated loops to investigate the diagnostic potential of chromospheric emission from small-scale events. Methods. The Mg II h and k, Ca II H and K, Ca II 854.2 nm, and Hα and Hβ chromospheric lines were synthesised from various RADYN models of coronal loops subject to electron beams of nanoflare energies. The contribution function to the line intensity was computed to better understand how the atmospheric response to the non-thermal electrons affects the formation of spectral lines and the detailed shape of their spectral profiles. Results. The spectral line signatures arising from the electron beams highly depend on the density of the loop and the lower cutoff energy of the electrons. Low-energy (5 keV) electrons deposit their energy in the corona and transition region, producing strong plasma flows that cause both redshifts and blueshifts of the chromospheric spectra. Higher-energy (10 and 15 keV) electrons deposit their energy in the lower transition region and chromosphere, resulting in increased emission from local heating. Our results indicate that effects from small-scale events can be observed with ground-based telescopes, expanding the list of possible diagnostics for the presence and properties of nanoflares.

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“…M1-10. Sub-A class (Glesener et al, 2017;Cooper et al, 2021) flares have been observed, as have flares > X10 (e.g., Emslie et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Interrogating solar flare loop models with IRIS observations 1: Overview of the models, and mass flows

Kerr

2022

Front. Astron. Space Sci.

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Solar flares are transient yet dramatic events in the atmosphere of the Sun, during which a vast amount of magnetic energy is liberated. This energy is subsequently transported through the solar atmosphere or into the heliosphere, and together with coronal mass ejections flares comprise a fundamental component of space weather. Thus, understanding the physical processes at play in flares is vital. That understanding often requires the use of forward modelling in order to predict the hydrodynamic and radiative response of the solar atmosphere. Those predictions must then be critiqued by observations to show us where our models are missing ingredients. While flares are of course 3D phenomenon, simulating the flaring atmosphere including an accurate chromosphere with the required spatial scales in 3D is largely beyond current computational capabilities, and certainly performing parameter studies of energy transport mechanisms is not yet tractable in 3D. Therefore, field-aligned 1D loop models that can resolve the relevant scales have a crucial role to play in advancing our knowledge of flares. In recent years, driven in part by the spectacular observations from the Interface Region Imaging Spectrograph (IRIS), flare loop models have revealed many interesting features of flares. For this review I highlight some important results that illustrate the utility of attacking the problem of solar flares with a combination of high quality observations, and state-of-the-art flare loop models, demonstrating: 1) how models help to interpret flare observations from IRIS, 2) how those observations show us where we are missing physics from our models, and 3) how the ever increasing quality of solar observations drives model improvements. Here in Paper one of this two part review I provide an overview of modern flare loop models, and of electron-beam driven mass flows during solar flares.

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NuSTAR observations of a repeatedly microflaring active region

Cited by 23 publications

References 60 publications

The First Survey of Quiet Sun Features Observed in Hard X-Rays With NuSTAR

The First Survey of Quiet Sun Features Observed in Hard X-Rays With NuSTAR

Chromospheric emission from nanoflare heating in RADYN simulations

Interrogating solar flare loop models with IRIS observations 1: Overview of the models, and mass flows

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