Subsecond Spikes in Fermi GBM X-Ray Flux as a Probe for Solar Flare Particle Acceleration

Abstract

Solar flares are known to release a large amount of energy into accelerating electrons. Studying small timescale (≤2s) fluctuations in nonthermal X-ray flux offers the opportunity to probe the nature of those acceleration mechanisms. By comparing the durations, differences in timing between energy bands, and the periodicity of these spikes against the relevant timescales called for by various acceleration mechanisms, a test for each mechanism’s validity can be made. This work details the analysis of fast fluctuations in Fermi Gamma-ray Burst Monitor (Fermi GBM) data from two M9.3 class solar flares that occurred on SOL2011-07-30 and SOL2011-08-04. This study shows the usefulness of Fermi GBM data as a means of examining these small timescale spikes and presents a rigorous method of identifying, counting, and measuring the temporal properties of these subsecond X-ray spikes. In the two flares examined we found spikes to primarily occur in spans of 60–100 s in the impulsive phase. The relative spike intensity averaged between 6% and 28% when compared to the slowly varying component of the X-ray flux. The average spike durations were 0.49 and 0.38 s for the 2 flares. The spike duration distribution for the SOL2011-08-04 flare was found to follow a power law with a −1.2 ± 0.3 index. Of the three spiking intervals identified, only one was found to have a periodicity, showing significant power at the 1.7 ± 0.1 Hz frequency.