Sources of Quasi-Periodic Pulses in the 18 August 2012 Flare

TL;DR

This study investigates the spatial and spectral properties of quasi-periodic pulses during the 2012 solar flare, revealing their likely origin in modulation of energy release processes and providing detailed plasma parameters of the sources.

Contribution

It presents new multi-instrument observations of QPPs in X-ray and microwave emissions, identifying their source locations and proposing a modulation mechanism for their generation.

Findings

QPPs had approximately ten-second periods in X-ray and microwave emissions.

X-ray source was located above the limb near EUV loop system legs.

Microwave sources were at footpoints of different loop systems.

Abstract

We analyzed spatial and spectral characteristics of quasi-periodic pulses (QPP) for the 18 August 2012 limb are, using new data from a complex of spectral and imaging instruments developed by the Siberian Solar Radio Telescope team and the Wind/Konus gamma-ray spectrometer. A sequence of broadband pulses with periods of approximately ten seconds were observed in X-rays at energies between 25 keV and 300 keV, and in microwaves at frequencies from a few GHz up to 34 GHz during an interval of one minute. The QPP X-ray source was located slightly above the limb where the south legs of large and small EUV loop systems were close to each other. Before the QPPs the soft X-ray emission and the Ramaty High Energy Solar Spectroscopic Imager signal from the energy channels below 25 keV were gradually arising for several minutes at the same location. It was found that each X-ray pulse showed the soft-hard-soft behavior. The 17 and 34 GHz microwave source were at footpoints of the small loop system and the source emitting in the 4.2 {7.4 GHz band in the large one. The QPPs were probably generated by modulation of acceleration processes in the energy release site. Analyzing radio spectra we determined the plasma parameters in the radio sources. The microwave pulses could be explained by relatively weak variations of the spectrum hardness of emitting electrons.