About Yohkoh > Yohkoh Instruments > this page

HXT is a Fourier synthesis type imager consisting of 64 bi-grid modulation subcollimators (SC's). Each SC has a different pitch and/or a position angle of collimator grids, together with a NaI (Tl) scintillation crystal and a detector photomultiplier located behind the SC. The number of hard X-ray photons passing through a single SC is periodically modulated with respect to the incident angle, which gives a modulation pattern of the corresponding SC, and count rate data obtained by each detector which can be regarded as a spatial Fourier component (+ DC level) of a hard X-ray image. When a flare-mode is triggered, a set of 64 hard X-ray count rate data is accumulated every 0.5 s (= the highest temporal resolution) in four energy bands between 14 and 93 keV (L, M1, M2, and H bands, respectively) and is transferred from HXT to the Data Processor (DP). The data are then telemetered down to the ground and hard X-ray images can be synthesized using image restoration procedures such as the Maximum Entropy Method (MEM). The field-of-view (FOV) of HXT is about 35 by 35 arcminutes, i.e. covering the whole Sun. This means that HXT can detect hard X-rays of flares regardless of their position on the Sun without re-pointing the spacecraft. The basic image synthesis FOV of HXT is 2.1 by 2.1 arcminutes with the angular resolution as high as approximately 5 arcseconds. A detailed description on the overview of the instrument is given by Kosugi et al. (1991). See Kosugi et al. (1992) for the in-orbit performance of HXT as well as some initial results.


HXT Figures (click to enlarge).

HXT spectral response.