Aims. We aim to constrain the acceleration, injection, and transport processes of flare-accelerated energetic electrons by comparing their characteristics at the Sun with those injected into interplanetary space. Methods. We have identified 17 energetic electron events well-observed with the SEPT instrument aboard STEREO which show a clear association with a hard X-ray (HXR) flare observed with the RHESSI spacecraft. We compare the spectral indices of the RHESSI HXR spectra with those of the interplanetary electrons. Because of the frequent double-power-law shape of the in situ electron spectra, we paid special attention to the choice of the spectral index used for comparison. Results. The time difference between the electron onsets and the associated type III and microwave bursts suggests that the electron events are detected at 1 AU with apparent delays ranging from 9 to 41 min. While the parent solar activity is clearly impulsive, also showing a high correlation with extreme ultraviolet jets, most of the studied events occur in temporal coincidence with coronal mass ejections (CMEs). In spite of the observed onset delays and presence of CMEs in the low corona, we find a significant correlation of about 0.8 between the spectral indices of the HXR flare and the in situ electrons. The correlations increase if only events with significant anisotropy are considered. This suggests that transport effects can alter the injected spectra leading to a strongly reduced imprint of the flare acceleration. Conclusions. We conclude that interplanetary transport effects must be taken into account when inferring the initial acceleration of solar energetic electron events. Although our results suggest a clear imprint of flare acceleration for the analyzed event sample, a secondary acceleration might be present which could account for the observed delays. However, the limited and variable pitch-angle coverage of SEPT could also be the reason for the observed delays.
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Observations of Magnetic Reconnection and Particle Acceleration Locations in Solar Coronal Jets
Abstract We present a multiwavelength analysis of two flare-related jets on 2014 November 13, using data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), the Reuven High Energy Solar Spectroscopic Imager (RHESSI), the Hinode/X-ray Telescope (XRT), and the Interface Region Imaging Spectrograph (IRIS). Unlike most coronal jets, where hard X-ray (HXR) emissions are usually observed near the jet base, in these events HXR emissions are found at several locations, including in the corona. We carry out the first differential emission measure analysis that combines both AIA (and XRT, when available) bandpass filter data and RHESSI HXR measurements for coronal jets, and obtain self-consistent results across a wide temperature range and into nonthermal energies. In both events, hot plasma first appears at the jet base, but as the base plasma gradually cools, hot plasma also appears near the jet top. Moreover, nonthermal electrons, while only mildly energetic, are found in multiple HXR locations and contain large amounts of total energy. In particular, the energetic electrons that produce the HXR sources at the jet top are accelerated near the top location, rather than traveling from a reconnection site at the jet base. This means that there is more than one particle acceleration site in each event. Jet velocities are consistent with previous studies, including the upward and downward velocities around ∼200 km s −1 and ∼100 km s −1 , respectively, and fast outflows of 400–700 km s −1 . We also examine the energy partition in the later event, and find that the nonthermal energy in the accelerated electrons is most significant compared to the other energy forms considered. We discuss the interpretations and provide constraints on the mechanisms for coronal jet formation.
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- Award ID(s):
- 1752268
- NSF-PAR ID:
- 10433579
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 943
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 180
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/aca654
