Location of Decimetric Pulsations in Solar Flares

TL;DR

This study examines the spatial relationship between coronal X-ray sources and decimetric pulsations in solar flares, revealing that radio emissions originate significantly above the X-ray sources and are likely emitted from a current sheet.

Contribution

It provides the first detailed spatial analysis linking decimetric pulsations to their likely origin in a current sheet above the flare's coronal X-ray source.

Findings

Radio pulsations originate 30-240 Mm above X-ray sources.

Radio emission altitude increases with decreasing frequency.

Pulsations are consistent with emission from a current sheet.

Abstract

This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nancay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30 - 240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source.