fl189.takakura05 Posted: 28-Aug-94 Updated: 3-Feb-95, 30-Sep-95 Events specified: Flares of 2-Nov-91 06:44, 15-Nov-91 22:35, 3-Dec-91 16:31, 16-Dec-91 19:22, 14-Feb-92 23:04, 8-Jul-92 09:42, 10-Sep-92 22:30
T.Takakura
Motivation: Spectra of hard X-rays from one or both of foot points of impulsive loop flares seem to frequently show a better fit to extremely hot thermal spectrum than a power law. In order to verify the above tendency, the spectra for the impulsive bursts which have a sufficient flux for the imaging without much ambiguity in H-band are investigated. The error for the spectral index is estimated by simulations.
Update 30-Sep-95
THIS PAPER HAS BEEN PUBLISHED IN PASJ, 47,355,1995.
Imaging Spectra of Hard X-Rays from the Footpoints of Solar Impulsive Loop Flares
Tatsuo Takakura, Takeo Kosugi, Taro Sakao, Kazuo Makishima, Mika Inda-Koide, and Satoshi Masuda
Abstract:
The imaging spectra of hard X-rays emitted from one or both footpoints of solar impulsive loop flares seem to frequently show a better fit to an extremely hot thermal spectrum, on the order of 10^8 K, than to a power-law spectrum, in the main phase of the bursts. In the present study this tendency has been verified by the spectra of nine impulsive bursts having a sufficient flux for reliable imaging in the H-band (52.7-92.8 keV) of the hard X-ray telescope (HXT) aboard the Yohkoh spacecraft. The spectral indices at the footpoints were derived from the hard X-ray images in four energy bands of the HXT; their reliability was verified by mapping simulations. Since the X-ray spectrum depends on the location in the X-ray loop, the spectrum of the total flux is generally different from the spatially resolved spectra. The imaging spectrum is thus crucial for studying the nature of the electrons emitting hard X-rays. The heat conduction of an extremely hot quasi-thermal plasma seems to play an essential role in impulsive loop flares.
Update 3-Feb-95
Paper submitted to PASJ, Jan. 27,1995
Imaging Spectra of Hard X-rays from Footpoints of Solar Impulsive Loop Flares
Tatsuo Takakura and HXT team
Abstract
Imaging spectra of hard X-rays emitted from one or both footpoints of solar impulsive loop flares seem to frequently show a better fit to an extremely hot thermal spectrum, of the order of $10^8$ K, than a power law spectrum, in the main phase of the bursts. In the present study, this tendency is verified by the spectra of nine impulsive bursts which have a sufficient flux for a reliable imaging in H-band (52.7-92.8 Kev) of hard X-ray telescope (HXT) aboard the Yohkoh spacecraft. The spectral indexes at the footpoints are derived from the hard X-ray images in four energy bands of the HXT, and their reliability is verified by simulations of mapping. The X-ray spectrum depends on the location in the X-ray loop, so that the spectrum of the total flux is generally different from the spatially resolved spectra. Imaging spectrum is thus crucial for the study of the nature of the electrons emitting hard X-rays.