Subsecond pulsations in hard X-rays of August 19, 1998 flare according to BATSE/CGRO data

Abstract

Detection of ms-spikes and quasi-periodic subsecond pulsations in the solar flare hard X-rays (HXR) provides useful information about the processes of electron acceleration and transport along the flare magnetic loops. To search for HXR pulsations, we processed the data of BATSE/CGRO spectrometer of high temporal resolution 0.016 s and 0.064 s. BATSE energy range is about 20 keV – 1 MeV. For the powerful solar flare SOL1998:08:19T21:39:21 the FFT and wavelet analysis show the presence of HXR pulsations of ∼ 0.16 – 0.25 s. BATSE data was analyzed for six energy channels 28.8 – 33.1 keV, 37.1 – 41.8 keV, 46.6 – 55.8 keV, 55.8 – 64.6 keV, 64.6 – 74.0 keV, and 74.0 – 99.1 keV. HXR-spikes were detected. The spike shape is practically triangular with FWHM about 100 ms. Simulations of kinetic models of electron transport with short pulses showed that when the duration of an individual spike is longer than ∼ 80 ms, the smearing of pulses practically does not occur. Injection pulses shorter than 30 – 60 ms are not preserved even with a strongly anisotropic distribution of accelerated electrons and a small gradient of the magnetic field. In the isotropic case at the looptop, the decay phase of the X-ray spikes becomes longer compared to the rising phase which is not true for the anisotropic case. The pulse smearing effect is stronger for the softer energy spectra of accelerated electrons.