Subsecond Hard X-Ray Spikes from Solar Flares: Limitations on the Electron Acceleration Mechanism

• Published in: Geomagnetism and aeronomy 2021-12, Vol.61 (8), p.1093-1100
• Main Authors: Charikov, Yu. E., Sklyarova, E. M., Shabalin, A. N.
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Geophysics/Geodesy
• ISSN: 0016-7932; 1555-645X
• DOI: 10.1134/S001679322108003X

The X-ray spike structure for solar flares recorded by the CGRO/BATSE spectrometer is discussed, and the kinetics of accelerated electrons propagating in the plasma of a magnetic loop with a spike temporal structure is simulated. The time resolution of the BATSE full-Sun spectrometer varied from 0.016 to 2.048 s during the flare. The total energy range 20 keV–1 MeV was divided into 16 channels. The spike structure of hard X-ray radiation is considered for three powerful flares: M1.4 SOL1991-12-25, M7.8 SOL1991-12-28, and Х12 SOL1991-06-06. The X-ray time profiles recorded with a time resolution of 16 ms represent a sequence of numerous pulses (spikes) with a duration of about 0.1 s. The growth and decay times of the spike are approximately the same, and the profiles of many spikes are nearly triangular. No strict temporal correspondence of spikes of different energies was revealed with such a resolution. Modeling of the propagation of a sequence of accelerated electron beams in the plasma of flare loops confirms the preservation of a similar spike structure of the hard X-ray radiation generated in the footpoints of the loops. Moreover, the pulse structure is preserved independently of the pitch-angular distribution of electrons and the loop plasma parameters. In the coronal part of the loop (looptop), hard X-ray spikes are generated only in the case of increase in plasma density. The spike structure of accelerated electrons is discussed within the so-called bursty reconnection model.