Non-thermal broadening of coronal emission lines in the onset phase of solar flares and CMEs

Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK e-mail: hrm@mssl.ucl.ac.uk

Received: 14 April 2005
Accepted: 3 August 2005

Abstract

The non-thermal broadening of soft X-ray emission lines is commonly seen during the early stages of solar flares and is thought to be associated with either the initial flare energy release or the evaporation of chromospheric plasma. Here we investigate the magnitude of non-thermal broadening for a sample of 12 flares associated with both eruptive and non-eruptive events, i.e. those with and without associated coronal mass ejections (CMEs), using the Bragg Crystal Spectrometer (BCS) on the Yohkoh spacecraft. The maximum non-thermal broadening of the eruptive flares was found to be on average lower than for the flares which were not associated with CMEs. There was no evidence of any relationship between the maximum non-thermal broadening and the initial CME speed.