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

[Abridged]We present analysis of a pair of unusually energetic coronal hardX-ray (HXR) sources detected by RHESSI during the impulsive phase of an X3.9class solar flare on 2003 November 3, which simultaneously shows two intensefootpoint (FP) sources. A distinct loop top (LT) coronal source is detected upto ~150 keV and a second (upper) coronal source up to ~80 keV. These photonenergies are much higher than commonly observed in coronal sources and posegrave modeling challenges. The LT source in general appears higher in altitudewith increasing energy and exhibits a more limited motion compared to theexpansion of the thermal loop. The high energy LT source shows an impulsivetime profile and its nonthermal power law spectrum exhibits soft-hard-softevolution during the impulsive phase, similar to the FP sources. The uppercoronal source exhibits an opposite spatial gradient and a similar spectralslope compared to the LT source. These properties are consistent with the modelof stochastic acceleration of electrons by plasma waves or turbulence. However,the LT and FP spectral index difference (varying from ~0-1) is much smallerthan commonly measured and than that expected from a simple stochasticacceleration model. Additional confinement or trapping mechanisms of highenergy electrons in the corona are required. Comprehensive modeling includingboth kinetic effects and the macroscopic flare structure may shed light on thisbehavior. These results highlight the importance of imaging spectroscopicobservations of the LT and FP sources up to high energies in understandingelectron acceleration in solar flares. Finally, we show that the electronsproducing the upper coronal HXR source may very likely be responsible for thetype III radio bursts at the decimetric/metric wavelength observed during theimpulsive phase of this flare.

Impulsive Phase Coronal Hard X-ray Sources in an X3.9 Class Solar Flare