fl224.tsuneta15 Posted: 17-Jan-96 Updated: 3-Feb-96, 26-Apr-96, 18-May-96, 20-Sep-96, 10-Nov-96, 27-Jan-97 Events specified: See text
by S. Tsuneta
The detailed temperature structure of the 1992 February 21 flare was done. In the same way, the temperature structure of the impulsive limb flares will be studied in detail in this project. The events to be analyzed include
91/12/02 92/01/13 (The Masuda flare) 92/02/06 92/02/17 92/04/01 92/10/04 92/11/05 93/02/17 93/03/16.
The crude temperature analysis had been done in Masuda papers, but no detailed analysis has not yet been done. The relation between the temperature structures and the hard X-ray sources including the loop top source is one of the interesting research topics in this project.
fl208.ohyama03 Temperature and emission measure structure of X-ray plasmoid ejection in eruptive flares
The following paper was submitted to ApJ:
MOVING PLASMOID AND FORMATION OF NEUTRAL SHEET IN A SOLAR FLARE
S. Tsuneta
Abstract A spectacular erupting feature with a plasmoid-like structure is observed before and during the solar flare that occurred on the limb on 1991, December 2 with the {\it Yohkoh} soft X-ray telescope. The rise of a loop structure starts $\sim$10 min before the flare, evolving to a plasmoid-like structure in the impulsive phase of the flare. The speed of the rising loop (plasmoid) is almost constant ($\sim$96 km s$^{-1}$) throughout the observation. A clear X-shaped structure is formed underneath the rising plasmoid, and a bright soft X-ray loop is formed below the X-point. The X-shaped structure indicates a magnetic neutral point with a large-scale magnetic separatrix structure. Inverse-V-shaped high-temperature ridges are located above the soft X-ray loop and below the X-point. These are reconnected loops heated by slow shocks. A moving high-temperature (15MK) source is found, coincident in position with the rising structure above the X-point. A hard X-ray source (33--53 keV) is located at the top of the soft X-ray flare loop. These two compact high-temperature sources located above and below the X-point would be formed by fast shocks due to the symmetric reconnection outflows both upward and downward from the X-point. The eruption preceding the flare appears to create the X-point and drive magnetic reconnection.
Update 10-Nov-96
The following paper was accepted by ApJ:
HOT AND SUPER-HOT PLASMAS ABOVE AN IMPULSIVE FLARE LOOP
Saku Tsuneta, Satoshi Masuda, Takeo Kosugi, Jun Sato
Update 20-Sep-96
The paper in previous report has not yet submitted. The detailed analysis still goes on. An interesting discovery is that 1. the hot ridge structure as has been observed for LDE flares and the 1992 Jan 13 impulsive flare was also confirmed in this flare, and that 2. a new hot source located around the erupting plasmoid is found. This hot source moves upward with the plasmoid, and may be related to the upward outflow.
Update 18-May-96
The following paper on the erupting feature of the 1991 December 2 flare is being written, and will be submitted soon.
PLASMOID RISE AND FORMATION OF NEUTRAL SHEET IN A SOLAR FLARE
by S. Tsuneta
ABSTRACT A spectacular erupting feature with plasmoid-like structure is observed before and during a solar flare that occurred on the limb on 1991, December 2. The loop expansion starts several minutes before the flare, evolving to the plasmoid-like structure in the impulsive phase of the flare. A clear X-shaped structure is formed underneath the rising plasmoid, and the bright soft X-ray loop is formed below the X-point. The rise speed of the initial expanding loop and the plasmoid is almost constant (96 km s$^{-1}$) throughout the flare, and the rise speed of the soft X-ray loop is about 11 km s$^{-1}$. The temperature maps show that the region above the soft X-ray loops has the highest temperature. These observations show that the formation of the X-point driven by the rise of the loop-structure and subsequent magnetic reconnection is responsbile for the flare.
Update 26-Apr-96
The following paper will be submiited to ApJ soon.
HOT AND SUPER-HOT PLASMAS ABOVE AN IMPULSIVE FLARE LOOP
Saku Tsuneta, Satoshi Masuda, Jun Sato, Takeo Kosugi
ABSTRACT We report the discovery of a high temperature source above the soft X-ray loop of the impulsive limb flare on 1992 January 13 with the {\it Yohkoh} Soft X-ray Telescope (SXT). The hot source coincides in position with the loop-top impulsive hard X-ray source, and continues to sit above the soft X-ray flare loop throughout the flare. The single high temperature source in the initial phase evolves to the two high temperature (15--20 MK) ridge structures in the peak and decay phases, and the compact hard X-ray source appears to be located in between the high temperature ridges. The loop-top hard X-ray source has effective temperature of 100--150MK (super-hot source) and total emission measure of $\sim$10$^{-4}$ of the hot source. The geometrical relationship between the super-hot and the hot sources indicates that (1) the hot source is heated by the slow shocks associated with magnetic reconnection, and that (2) the super-hot source is heated with the bow shock due to the collision of the supersonic downward outflow with the reconnected flux tube. The extremely small emission measure of the super-hot source indicates a narrow outflow jet in between the slow shocks. These observations suggest that there is no essential difference between the compact-loop (impulsive) and long duration (LDE) flares. Non-thermal electron acceleration appears to be causally related to the formation of the bow shock rather than the slow shocks.
Update 3-Feb-96
Detailed analysis is being done on the 1992 Jan 13 flare (Masuda flare). The abstract for the Bath meeting is added below. The full paper is being written, and will be submitted to ApJ shortly.
Bath meeting abstract
Hot and Super Hot Plasmas above the Flare Loop
Saku Tsuneta Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan Satoshi Masuda STE Laboratory, Nagoya University, Toyokawa, Aichi 442, Japan Jun Sato and Takeo Kosugi National Astronomical Observatory, Mitaka, Tokyo 181, Japan
We have discovered the compact high temperature source with temperature as high as 30 MK (hereafter referred to as hot plasma) for the Masuda flare (1992 January 13 flare). The hot source coincides in position with the hard X-ray source above the loop top in the impulsive phase (Masuda et al., Nature, 371, 495, 1994), and continues to stay above the loop top with increasing temperature well after the disappearance of the hard X-ray source. The hard X-ray source is seen only when the temperature of the hot source is lower (15 MK). We interpret that the hot source is due to the heating by magnetic reconnection (slow shocks), because the hot source sits above the flare loop throughout the flare.
We assume that the hard X-rays are of thermal origin (hereafter referred to as super hot plasma): the temperature is 100--150 MK with emission measure 1/1000 of the hot source seen with SXT. The super hot plasma is not heated by the slow shocks, which heat the hot plasma. Instead, we suggest that the super hot plasma is heated by the perpendicular (fast) shock associated with fast reconnection outflow. In the initial phase where the temperature of the hot source is low, the resulting high Mach number of the outflow suggests intense shock heating. The Mach number gradually decreases with increasing temperatures, resulting in the disappearance of the shock {\it ie}. the disappearance of the loop-top hard X-ray source. This scenario predicts and suggests the following: (1) The loop top hard X-rays tend to be seen for flares/phases with lower loop-top temperatures. (2) The fast reconnection outflow is highly filamentary, and the super hot plasma occupies a few \% of the hot source volume. (3) The non-thermal electron acceleration is related to the formation of the fast shock rather than the slow shocks.