English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We report the detection of emission from a non-thermal electron distributionin a small solar microflare (GOES class A5.7) observed by the NuclearSpectroscopic Telescope Array (NuSTAR), with supporting observation by theReuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The flaringplasma is well accounted for by a thick-target model of accelerated electronscollisionally thermalizing within the loop, akin to the "coronal thick target"behavior occasionally observed in larger flares. This is the first positivedetection of non-thermal hard X-rays from the Sun using a direct imager (asopposed to indirectly imaging instruments). The accelerated electrondistribution has a spectral index of 6.3 +/- 0.7, extends down to at least 6.5keV, and deposits energy at a rate of ~2x1027 erg/s, heating the flare loop toat least 10 MK. The existence of dominant non-thermal emission in X-rays downto <5 keV means that RHESSI emission is almost entirely non-thermal, contraryto what is usually assumed in RHESSI spectroscopy. The ratio of non-thermal tothermal energies is similar to that of large flares, in contrast to what hasbeen found in previous studies of small RHESSI flares. We suggest that acoronal thick target may be a common property of many small microflares basedon the average electron energy and collisional mean free path. Futureobservations of this kind will enable understanding of how flare particleacceleration changes across energy scales, and will aid the push toward theobservational regime of nanoflares, which are a possible source of significantcoronal heating.

Accelerated electrons observed down to <7 keV in a NuSTAR solar microflare