Temporal Variations of X-Ray Solar Flare Loops: Length, Corpulence, Position, Temperature, Plasma Pressure, and Spectra

Abstract

The spatial and spectral properties of three solar flare coronal X-ray loops are studied before, during and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density and thermal pressure. We observe a decrease in the loop length, width and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to an increasing width. The volume variations are more pronounced than the position variations, often known as magnetic line contraction. We believe this is the first dedicated study of the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission and thermal pressure, with minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low β plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density, producing increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.

Soft X-ray emission in kink-unstable coronal loops

“…The apparent radius of the loop (the radius of the emitting plasma) varies as a function of time in our simulations (cf. Jeffrey & Kontar 2013). The width of the emitting region is initially smaller than that of the actual magnetic flux-rope, but increases quickly as the instability proceeds.…”

“…If our model had represented a real solar flare, these details would only be detectable as a fast initial increase in thickness and length of the flaring coronal loop (cf. Jeffrey & Kontar 2013), given the spatial resolution of the current X-ray instruments. Interestingly, the initial magnetic twist in the pre-flare flux-rope as perceived from the X-ray emission is much weaker than the highest twist at these instants.…”

Magnetic Shocks and Substructures Excited by Torsional Alfvén Wave Interactions in Merging Expanding Flux Tubes

“…The forcing terms manifest as terms in the momentum and energy equations. The flux tubes are constructed to match observed models (e.g., Verth et al 2011;Jeffrey & Kontar 2013) and stable multiple flux tubes are regularly observed in pressure equilibrium (e.g., Levine & Withbroe 1977;McGuire et al 1977;Malherbe et al 1983). Perturbations in such stable flux tubes are investigated in a large number of observational, numerical, and theoretical studies (see, for example, reviews cited in the Introduction).…”

High-temperature differential emission measure and altitude variations in the temperature and density of solar flare coronal X-ray sources

“…Svestka et al 1987;Tsuneta et al 1992;Švestka 1996;Gallagher et al 2002). Sometimes an initial decrease in altitude is followed by an increase in altitude after the impulsive phase of the flare (Sui & Holman 2003;Sui et al 2004;Veronig et al 2006;Liu et al 2009;Joshi et al 2009;Reznikova et al 2010;Gosain 2012;Jeffrey & Kontar 2013), and sometimes even more complicated motions are observed (e.g. Liu et al 2013).…”

“…Sub-arcsecond measurements of X-ray footpoint locations have been achieved using X-ray visibilities (see e.g. Kontar et al 2008Kontar et al , 2010Jeffrey & Kontar 2013), improving upon forward fitting a Gaussian source model to the RHESSI modulated lightcurves (e.g. Aschwanden et al 2002).…”