INVESTIGATING THE DIFFERENTIAL EMISSION MEASURE AND ENERGETICS OF MICROFLARES WITH COMBINED<i>SDO</i>/AIA AND<i>RHESSI</i>OBSERVATIONS

In this paper we present the differential emission measures (DEMs) of two sub-A class microflares observed in hard X-rays (HXRs) by the FOXSI-2 sounding rocket experiment, on 2014 December 11. The second FOXSI (Focusing Optics X-ray Solar Imager) flight was coordinated with instruments Hinode/XRT and SDO /AIA, which provided observations in soft X-rays (SXR) and Extreme Ultraviolet (EUV). This unique dataset offers an unprecedented temperature coverage useful for characterizing the plasma temperature distribution of microflares. By combining data from FOXSI-2 , XRT, and AIA, we determined a well-constrained DEM for the microflares. The resulting DEMs peak around 3MK and extend beyond 10MK. The emission measures determined from FOXSI-2 were lower than 10 26 cm −5 for temperatures higher than 5MK; faint emission in this range is best measured in HXRs. The coordinated FOXSI-2 observations produce one of the few definitive measurements of the distribution and the amount of plasma above 5MK in microflares. We utilize the multi-thermal DEMs to calculate the amount of thermal energy released during both the microflares as ∼ 5.0 × 10 28 ergs for Microflare 1 and ∼ 1.6 × 10 28 ergs for Microflare 2. We also show the multi-thermal DEMs provide a more comprehensive thermal energy estimates than isothermal approximation, which systematically underestimates the amount of thermal energy released.

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“…Using the best DEM solution, we calculate the thermal energy released based on Inglis & Christe (2014), which is given as:…”

Section: Thermal Energy Estimatesmentioning

confidence: 99%

FOXSI-2 Solar Microflares. I. Multi-instrument Differential Emission Measure Analysis and Thermal Energies

Athiray

Vievering

Glesener

et al. 2020

ApJ

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“…Schmelz et al 2011, Del Zanna 2013, microflares (e.g. Inglis & Christe 2014, Wright et al 2017) and flares (e.g. Hannah & Kontar 2013, Battaglia et al 2014, Simões et al 2015a).…”

Section: Introductionmentioning

confidence: 99%

The Spectral Content of SDO/AIA 1600 and 1700 Å Filters from Flare and Plage Observations

Simões

Reid

Milligan³

et al. 2019

ApJ

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The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the Transition Region and Coronal Explorer (TRACE) and Atmospheric Imaging Assembly (AIA 1600 and 1700Å) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without the knowledge of the spectral contribution to these UV filters, the use of these rich imaging datasets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300 to 1900Å from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600Å is dominated by the C IV 1550Å doublet (26%), Si I continua (20%), with smaller contributions from many other chromospheric lines such as C I 1561 and 1656Å multiplets, He II 1640Å, Si II 1526 and 1533Å. For the AIA 1700Å band, C I 1656Å multiplet is the main contributor (38%), followed by He II 1640 (17%), and accompanied by a multitude of other, weaker chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.

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“…An improvement over this would be simultaneous fitting of RHESSI and AIA data. Inglis & Christe (2014) performed such joint fitting on the low energy (thermal) component of microflares, but fitted any existing high-energy X-ray component separately.…”

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confidence: 99%

Multithermal Representation of the Kappa-Distribution of Solar Flare Electrons and Application to Simultaneous X-Ray and Euv Observations

Battaglia

Motorina

Kontar

2015

ApJ

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Acceleration of particles and plasma heating is one of the fundamental problems in solar flare physics. An accurate determination of the spectrum of flare energized electrons over a broad energy range is crucial for our understanding of aspects such as the acceleration mechanism and the total flare energy. Recent years have seen a growing interest in the kappa-distribution as representation of the total spectrum of flare accelerated electrons. In this work we present the kappa-distribution as a differential emission measure. This allows for inferring the electron distribution from X-ray observations and EUV observations by simultaneously fitting the proposed function to RHESSI and SDO/AIA data. This yields the spatially integrated electron spectra of a coronal source between less than 0.1 keV up to several tens of keV. The method is applied to a singleloop GOES C4.1 flare. The results show that the total energy can only be determined accurately by combining RHESSI and AIA observations. Simultaneously fitting the proposed representation of the kappa-distribution reduces the electron number density in the analysed flare by a factor of ∼ 30 and the total flare energy by a factor of ∼ 5 compared with the commonly used fitting of RHESSI spectra. The spatially integrated electron spectrum of the investigated flare between 0.043 keV and 24 keV is consistent with the combination of a low-temperature (∼ 2 MK) component and a hot (∼ 11 MK) kappa-like component with spectral index 4, reminiscent of solar wind distributions.

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INVESTIGATING THE DIFFERENTIAL EMISSION MEASURE AND ENERGETICS OF MICROFLARES WITH COMBINEDSDO/AIA ANDRHESSIOBSERVATIONS

Cited by 40 publications

References 50 publications

FOXSI-2 Solar Microflares. I. Multi-instrument Differential Emission Measure Analysis and Thermal Energies

FOXSI-2 Solar Microflares. I. Multi-instrument Differential Emission Measure Analysis and Thermal Energies

The Spectral Content of SDO/AIA 1600 and 1700 Å Filters from Flare and Plage Observations

Multithermal Representation of the Kappa-Distribution of Solar Flare Electrons and Application to Simultaneous X-Ray and Euv Observations

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