Detection of nanoflare-heated plasma in the solar corona by the FOXSI-2 sounding rocket

Ishikawa, Shin-­nosuke; Glesener, Lindsay; Krucker, S.; Christe, Steven; Buitrago-Casas, J. C.; Narukage, Noriyuki; Vievering, Juliana

doi:10.1038/s41550-017-0269-z

Cited by 68 publications

(75 citation statements)

References 22 publications

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“…Figure 7 (Left) compares the flaring and nonflaring DEMs of AR12234 (Microflare 2). The steep DEM power-law relation ∝ T −12 determined by (Ishikawa et al 2017), between log T = 6.6 to 7.0, reduces to ∝ T −5 during the flare phase. Figure 7 (Right) shows the microflare DEM subtracted from the quiet DEM with ∝ T −4 .…”

Section: Combined Dem Analysis Of Microflare Emissionmentioning

confidence: 87%

“…Although Microflare 1 shows less HXR emission during Target J, we do not have compelling evidence to unambiguously claim that for quiescent emission. For Microflare 2, we considered the quiet AR DEM established in Ishikawa et al (2017). Figure 7 (Left) compares the flaring and nonflaring DEMs of AR12234 (Microflare 2).…”

Section: Combined Dem Analysis Of Microflare Emissionmentioning

confidence: 99%

“…Joint observations in the extreme ultraviolet (EUV), soft X-rays (SXRs) and hard X-rays (HXRs) have been useful to determine the underlying temperature distribution of the hot coronal plasma (e.g. Ishikawa et al 2017;Wright et al 2017;Ishikawa & Krucker 2019). Current space instrumentation in the EUV and SXRs have limited sensitivity to plasma above 5MK (Winebarger et al 2012).…”

Section: Introductionmentioning

confidence: 99%

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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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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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Section: Combined Dem Analysis Of Microflare Emissionmentioning

confidence: 87%

Section: Combined Dem Analysis Of Microflare Emissionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…Blinkers were detected as the intensity enhancements in EUV/SXR lines (Harrison 1997;Chae et al 2000). Nanoflares were observed as EUV brightenings in the corona (Benz & Krucker 1998;Ishikawa et al 2017). Spicules were dynamic jet-like features in the chromosphere or corona (Pereira et al 2016;De Pontieu et al 2017).…”

Section: Discussionmentioning

confidence: 99%

Spectroscopic and imaging observations of small-scale reconnection events

Dong

Ning

2018

Monthly Notices of the Royal Astronomical Society

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We present spectroscopic and imaging observations of small-scale reconnection events on the Sun. Using the Interface Region Imaging Spectrograph (IRIS) observations, one reconnection event is first detected as IRIS jets with fast bi-directional velocities in the chromosphere and transition region, which are identified as non-Gaussian broadenings with two extended wings in the line profiles of Si iv, C ii, and Mg ii k. The magnetograms under the IRIS jets from Helioseismic and Magnetic Images exhibit magnetic flux cancellation simultaneously, supporting that the IRIS jets are driven by magnetic reconnection. The Atmospheric Imaging Assembly images also show an extreme ultraviolet (EUV) brightening which is shortly after the underlying IRIS jets, i.e., in the 131Å, 171Å, 193Å, 211Å, and 94Å channels, implying that the overlying EUV brightening in the corona is caused by the IRIS jets in the chromosphere and transition region. We also find another three reconnection events which show the same features during this IRIS observation. Our observational results suggest that the small-scale reconnection events might contribute to the coronal heating. The new result is that the process of magnetic reconnection is detected from the photosphere through chromosphere and transition region to the corona.

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“…In general, we do not expect these active regions to contain only a single temperature, as there is a broad base of literature finding multithermal distributions in active regions. Furthermore, the FOXSI -2 active region has been demonstrated by Ishikawa et al (2017) to be multithermal when consid- ering Hinode/XRT data alongside the FOXSI -2 data; temperatures of at least 3-15 MK were found. An isothermal fit to a multithermal temperature distribution picks out the temperature to which the instrument is the most sensitive.…”

Section: Solar Observations With Nustar and Foxsimentioning

confidence: 98%

Hard X-Ray Constraints on Small-scale Coronal Heating Events

Smith

Glesener

Klimchuk

et al. 2018

ApJ

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Much evidence suggests that the solar corona is heated impulsively, meaning that nanoflares may be ubiquitous in quiet and active regions (ARs). Hard X-ray (HXR) observations with unprecedented sensitivity >3 keV are now enabled by focusing instruments. We analyzed data from the Focusing Optics X-ray Solar Imager (FOXSI) rocket and the Nuclear Spectroscopic Telescope Array (NuSTAR) spacecraft to constrain properties of AR nanoflares simulated by the EBTEL field-line-averaged hydrodynamics code. We generated model X-ray spectra by computing differential emission measures for homogeneous nanoflare sequences with heating amplitudes H 0 , durations τ , delay times between events t N , and filling factors f . The single quiescent AR observed by FOXSI-2 on 2014 December 11 is well fit by nanoflare sequences with heating amplitudes 0.02 erg cm −3 s −1 < H 0 < 13 erg cm −3 s −1 and a wide range of delay times and durations. We exclude delays between events shorter than ∼900 s at the 90% confidence level for this region. Three of five regions observed by NuSTAR on 2014 November 1 are well fit by homogeneous nanoflare models, while two regions with higher fluxes are not. Generally, the NuSTAR count spectra are well fit by nanoflare sequences with smaller heating amplitudes, shorter delays, and shorter durations than the allowed FOXSI-2 models. These apparent discrepancies are likely due to differences in spectral coverage between the two instruments and intrinsic differences among the regions. Steady heating (t N = τ ) was ruled out with >99% confidence for all regions observed by either instrument.

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Detection of nanoflare-heated plasma in the solar corona by the FOXSI-2 sounding rocket

Cited by 68 publications

References 22 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

Spectroscopic and imaging observations of small-scale reconnection events

Hard X-Ray Constraints on Small-scale Coronal Heating Events

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