Coronal X-ray enhancements associated with H? filament disappearances

Abstract

A survey of soft X-ray images from Skylab has revealed a class of large-scale transient X-ray enhancements in the lower corona which are typically associated with the disappearance of Ha filaments away from active regions. Contemporary with the Ha filament disappearance, X-r@ emitting structures appeared at or near the filament location with shape and size resembling the filament. Eventually these structures faded, but the filament cavity was no longer obvious. Typically the peak of the X-ray event lagged the end of the filament disappearance by tens of minutes. The durations of the coronal X-ray enhancements were considerably longer than the associated Ha filament disappearances. Major flare effects, such as chromospheric brightenings, typically were not associated with these X-ray events.One event analyzed quantitatively had a peak temperature between 1.8 and 2.7 x 106 K, achieved a peak density of ~ 109 cm -3 and resulted in an enhancement in the plasma pressure over the conditions of the preexisting coronal cavity of at least a factor of 7. The mass of the coronal X-ray emitting material was about 10% that of the preexisting filament and the thermal energy of the coronal event was on the order of 1029 erg, about 10% of the mechanical energy of the Ha filament eruption. The event appeared to cool by radiative losses and not by thermal conduction. It is likely that the coronal enhancements are caused by heating of an excess of previously cooler material, either from the filament itself, or by compression of coronal material by a changing magnetic field.

Coronal Mass Ejections: Models and Their Observational Basis

“…(3) SXR brightenings Roy and Tang (1975) studied six flares and found that SXR bursts often accompany the preflare expansion of the filaments. Such a phenomenon was studied by several researchers (Pallavicini et al, 1975;Rust et al, 1975;Webb et al, 1976). As an extension, Simnett and Harrison (1985) studied the relation between the preflare activity and CMEs, and found that there is usually a weak SXR enhancement 15 -30 min prior to the linearly extrapolated onset time of the CMEs, which was called SXR precursors for CMEs.…”

Large-scale source regions of earth-directed coronal mass ejections

“…Filament eruptions, one of the earliest known forms of mass ejections from the Sun, are the near-surface activities that are most frequently associated with CMEs, and they have received considerable attention since the late 1900s (Webb et al 1976;Munro et al 1979;Webb & Hundhausen 1987;St Cyr & Webb 1991;Tandberg-Hanssen 1995;Zhang & Wang 2000;Gopalswamy 2003). They can erupt on different scales, from mini-filaments to AR filaments to long eruptive filaments.…”

On the Nature of the X-Ray Bright Core in a Stable Filament Channel

“…In addition to this, several other cases of stable filament channels with a hot, X-ray-emitting core inside the otherwise dark (in X-rays) cavities have been reported. 2 One interesting case was observed during the time interval from 05:48 to 23:20 UT on 2000 January 22, in which a long stable filament channel in the southern hemisphere was seen to light up in soft X-rays along the entire length of channel several times without catastrophically disrupting the channel (see first URL in footnote 2; see also Webb et al 1976 for earlier observations). Figures 1b and 1c show two soft X-ray images before and during the brightening.…”