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

Smith, David M.; Glesener, Lindsay; Klimchuk, J. A.; Bradshaw, S. J.; Vievering, Juliana; Hannah, I. G.; Christe, Steven; Ishikawa, Shin-­nosuke; Krucker, S.

doi:10.3847/1538-4357/aad380

Cited by 18 publications

(18 citation statements)

References 59 publications

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“…There is substantial literature on the detection of weak transient activity starting from early Yohkoh soft X-ray (e.g., Shimizu 1995) and Extreme ultraviolet Imaging Telescope (EIT) extreme ultraviolet (EUV) observations (e.g., Berghmans et al 1998) to observations from the Transition Region and Coronal Explorer (TRACE; e.g., Aschwanden et al 2000;Parnell & Jupp 2000), Ramaty High Energy Solar Spectroscopic Imager (RHESSI; e.g., Hannah et al 2008), Hinode's X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS; see Hinode Review Team 2019, and references therein); Atmospheric Imaging Assembly (AIA; e.g., Joulin et al 2016; Ulyanov et al 2019), Interface Region Imaging Spectrograph (IRIS; e.g., Peter et al 2014;Vissers et al 2015;Rouppe van der Voort et al 2016), Focusing Optics X-ray Solar Imager (FOXSI), and the Nuclear Spectroscopic Telescope Array (NuSTAR; Marsh et al 2018). Monte Carlo simulations of the statistical signatures of very weak events were presented by Dillon et al (2019).…”

Section: Introductionmentioning

confidence: 99%

Transient brightenings in the quiet Sun detected by ALMA at 3 mm

Nindos

Alissandrakis

Patsourakos

et al. 2020

A&A

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Aims. We investigate transient brightenings, that is, weak, small-scale episodes of energy release, in the quiet solar chromosphere; these episodes can provide insights into the heating mechanism of the outer layers of the solar atmosphere. Methods. Using Atacama Large Millimeter/submillimeter Array (ALMA) observations, we performed the first systematic survey for quiet Sun transient brightenings at 3 mm. Our dataset included images of six 87″ × 87″ fields of view of the quiet Sun obtained with angular resolution of a few arcsec at a cadence of 2 s. The transient brightenings were detected as weak enhancements above the average intensity after we removed the effect of the p-mode oscillations. A similar analysis, over the same fields of view, was performed for simultaneous 304 and 1600 Å data obtained with the Atmospheric Imaging Assembly. Results. We detected 184 3 mm transient brightening events with brightness temperatures from 70 K to more than 500 K above backgrounds of ∼7200 − 7450 K. All events showed light curves with a gradual rise and fall, strongly suggesting a thermal origin. Their mean duration and maximum area were 51.1 s and 12.3 Mm2, respectively, with a weak preference of appearing at network boundaries rather than in cell interiors. Both parameters exhibited power-law behavior with indices of 2.35 and 2.71, respectively. Only a small fraction of ALMA events had either 304 or 1600 Å counterparts but the properties of these events were not significantly different from those of the general population except that they lacked their low-end energy values. The total thermal energies of the ALMA transient brightenings were between 1.5 × 1024 and 9.9 × 1025 erg and their frequency distribution versus energy was a power law with an index of 1.67 ± 0.05. We found that the power per unit area provided by the ALMA events could account for only 1% of the chromospheric radiative losses (10% of the coronal ones). Conclusions. We were able to detect, for the first time, a significant number of weak 3 mm quiet Sun transient brightenings. However, their energy budget falls short of meeting the requirements for the heating of the upper layers of the solar atmosphere and this conclusion does not change even if we use the least restrictive criteria possible for the detection of transient brightenings.

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Section: Introductionmentioning

confidence: 99%

Transient brightenings in the quiet Sun detected by ALMA at 3 mm

Nindos

Alissandrakis

Patsourakos

et al. 2020

A&A

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“…Coronal loops outside of flares but at temperatures above 5-6 MK have been extensively observed and studied in the past. Most studies focused on demonstrating that these coronal loops were really the site of very hot plasma, with the detection of emission from single very hot lines (Ko et al 2009;Testa & Reale 2012), of very hot components in broad-band spectra (Miceli et al 2012), hard X-rays (McTiernan 2009Ishikawa et al 2017;Marsh et al 2018), and imaging from narrow-band EUV (Reale et al 2011;Brosius et al 2014) and broad-band X-rays (Porter & Klimchuk 1995;Reale et al 2009). Also emission measure reconstruction recovered small very hot components in active region loops (Petralia et al 2014;Parenti et al 2017;Ishikawa et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Impulsive Coronal Heating from Large-scale Magnetic Rearrangements: From IRIS to SDO/AIA

Reale

Testa

Petralia

et al. 2019

ApJ

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The Interface Region Imaging Spectrograph (IRIS) has observed bright spots at the transition region footpoints associated with heating in the overlying loops, as observed by coronal imagers. Some of these brightenings show significant blueshifts in the Si iv line at 1402.77Å (log T [K] ≈ 4.9). Such blueshifts cannot be reproduced by coronal loop models assuming heating by thermal conduction only, but are consistent with electron beam heating, highlighting for the first time the possible importance of non-thermal electrons in the heating of non-flaring active regions. Here we report on the coronal counterparts of these brightenings observed in the hot channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We show that the IRIS bright spots are the footpoints of very hot and transient coronal loops which clearly experience strong magnetic interactions and rearrangements, thus confirming the impulsive nature of the heating and providing important constraints for their physical interpretation.

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“…Recent instrumentation such as the Focusing Optics X-ray Solar Imager (FOXSI) rocket (Glesener et al 2016) made such observations of an active region. FOXSI observed a quiescent active region and X-ray spectra were modeled for nanoflare sequences with different characteristics such as heating amplitudes and durations (Marsh et al 2018). The FOXSI data were consistent with nanoflare sequences.…”

Section: Active Region Structure and Heatingmentioning

confidence: 56%

Observations of the Solar Corona from Space

et al. 2020

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Space observations of the atmosphere of the Sun, obtained in half a century of dedicated space missions, provide a well established picture of the medium and large-scale solar corona, which is highly variable with the level of solar activity through a solar cycle and evolves with the long-term evolution of the magnetic cycles. In this review, we summarize the physical properties and dynamics of the medium and large-scale corona, consisting primarily of active regions, streamers and coronal holes; describe the dependence of coronal patterns on the magnetic field patterns changing through the solar cycle and the properties of the regions of open magnetic flux channeling the solar wind; the ubiquitous presence of fluctuations in the outer corona; the rotational properties of the large-scale corona; and the persistent hemispheric asymmetries in the emergence of magnetic fields and the distribution of the coronal emission.

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

Cited by 18 publications

References 59 publications

Transient brightenings in the quiet Sun detected by ALMA at 3 mm

Transient brightenings in the quiet Sun detected by ALMA at 3 mm

Impulsive Coronal Heating from Large-scale Magnetic Rearrangements: From IRIS to SDO/AIA

Observations of the Solar Corona from Space

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