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Astron. Astrophys. 364, 859-872 (2000)

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2. Instrumentation

The Bragg Crystal Spectrometer on board Yohkoh (BCS, Culhane et al. 1991; Lang et al. 1993) is a full Sun instrument. It uses four bent crystals to observe simultaneously the spectrum of soft X-ray lines in four narrow wavelength ranges centered around the principle resonance lines of He-like SXV , CaXIX , FeXXV and H-like FeXXVI . Temperature of maximum formation and the detector wavelength ranges ([FORMULA]) that cover the BCS ions are shown in Table 1. Temperatures of maximum formation ([FORMULA]) are taken from Arnaud & Rothenflug (1985) throughout this article. In this paper we examine only the CaXIX data. The SXV data were unfortunately contaminated by the many active regions on the disk, hence the spectra in the early phases of the flare showed two distinct components. CaXIX data was used in preference to the iron lines because it is closer in temperature to the response of SXT.


Table 1. Temperature of maximum formation ([FORMULA]) and the detector wavelength ranges ([FORMULA]) that cover the BCS ions.

The Soft X-ray Telescope (SXT, Tsuneta et al. 1991) is a grazing incidence X-ray telescope operating in the wavelength range 2[FORMULA]70Å. Plasma diagnostics are achieved by formulating the ratios of images taken with various broad band filters which have different signal responses at different temperatures. In flare mode SXT takes a full resolution image in each filter every two seconds and cycles through the four different filters. The spatial resolution is 5 arc-seconds (pixel size 2.5 arc-seconds).

The Hard X-ray Telescope (HXT, Kosugi et al. 1991) is a Fourier synthesis imager of 64 elements and 4 energy channels which operate in the range [FORMULA] to [FORMULA]. Each subcollimator measures a spatially-modulated incident photon count, which is Fourier-transformed into an image. During flare mode the temporal resolution is 0.5 seconds.

The Transition Region and Coronal Explorer (TRACE, Handy et al. 1999; Schrijver et al. 1999) employs multi-wavelength optics and a lumogen coated CCD to record three EUV wavelengths and several UV wavelengths. TRACE views plasma at selected temperatures from 6000K to 10MK with a maximum field of view of 8.5 arc-minutes square, spatial resolution of 1 arc-second (0.5 arc-second pixels) and a typical temporal resolution of less than a minute. For this flare study the TRACE was observing with all of its EUV filters, namely 171 Å(FeIX , [FORMULA]), 195 Å(FeXII , [FORMULA]) and 284 Å(FeXV , [FORMULA]) and with the Lyman [FORMULA] (L[FORMULA]) filter at 1216 Å. The cadence in the EUV images was typically 160 seconds with approximately 6 seconds exposure times. The cadence at L[FORMULA] was typically 30 seconds with 0.7 second exposures. TRACE observations of the flaring active region began at 18:00UT and continued for several hours.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001