EDP Sciences
Free access
Volume 379, Number 2, November IV 2001
Page(s) 616 - 621
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20011342

A&A 379, 616-621 (2001)
DOI: 10.1051/0004-6361:20011342

The timing of non-thermal soft X-ray emission line broadenings in solar flares

N. D. R. Ranns, L. K. Harra, S. A. Matthews and J. L. Culhane

Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK

(Received 19 October 2000 / Accepted 24 September 2001)

We study 59 solar limb flares using the Bragg Crystal Spectrometer (BCS) on Yohkoh and the Burst and Transient Source Experiment (BATSE) to investigate the relative timings between the Hard X-Ray (HXR) emission and the observed non-thermal broadenings of X-ray emission lines ( $V\sb{\rm nt}$). We show that the duration of the HXR flux rise to maximum emission affects the relative timing of the main $V\sb{\rm nt}$ peak with respect to the main HXR peak. In $\approx$20% of the flares studied, secondary peaks in $V\sb{\rm nt}$ are observed. These are always associated with a strong HXR pulse and usually occur after the associated HXR pulse. There are also flares that show a relationship between the decay times of $V\sb{\rm nt}$ and HXR flux. These results are conducive to a causal relationship between the HXR flux and $V\sb{\rm nt}$. We divided the sample of flares into two classes, gradual rise and impulsive rise, depending on the shape of the HXR lightcurve up to maximum emission. We show that the $V\sb{\rm nt}$ behaviour differs in the two classes. The implications are discussed with a view to understanding the mechanism of $V\sb{\rm nt}$ generation.

Key words: Sun: flares -- Sun: general -- Sun: X-rays, gamma rays

Offprint request: S. A. Matthews, sam@mssl.ucl.ac.uk

© ESO 2001