Instrument Description

The OXS is a large, flat Bragg Crystal panel mounted in front of MM No. 1. Different crystals and multilayer coatings provide high-resolution imaging spectroscopy, and allow the study of highly ionized plasmas with appreciable angular extent ( $\sim1^{\circ}$) and which emit a broad range of line spectra from oxygen through iron. The spectra of point sources can also be studied with unprecedented resolution.

One side of the OXS panel is completely covered with $23\times63$ mm² LiF(220) crystals, while the other side is covered partly with $20\times60$ mm² RAP(001) crystals and partly with a multilayer (ML) of $60\times60$ mm² Si(111) crystals coated with $\sim$70 periods of Co/C. The coated Si crystals allow simultaneous spectroscopy in two separate wavelength bands: the softer x-ray wavelengths are reflected in the multilayer coatings and the harder x-ray wavelengths are reflected in the substrate (Si-111). Table 7 summarizes the properties of the OXS. The effective area of the OXS, when combined with the LEPC focal plane detector (the normal configuration) is shown in Figure 55.

 

Table 7: OXS Parameters

Crystal	LiF	Si	RAP	ML
Observable H- & He-like lines	Fe	S & Ar	O
Bragg angle for He-like lines	41$^{\circ}$	50$^{\circ}$ & 39$^{\circ}$	57$^{\circ}$
Wavelength Range (nm)	0.17-0.25	0.27-0.54	1.54-2.26	4.4-7.1
Energy Range (keV)	5.0-7.4	2.3-4.6	0.55-0.81	0.175-0.28
Rocking Curve Width	2.5$^{\prime}$	1.6$^{\prime}$	7$^{\prime}$	40$^{\prime}$
Energy Resolution (E/$\Delta$E)	1250	3200	770	80
Peak Reflectivity	21%	35%	2%	12-22%
Non-X-ray Bgd. (c s-1 keV-1 pixel-1)	$\sim 9\times10^{-5}$	$\sim 9\times10^{-5}$	$\sim 9\times10^{-5}$	$\sim 9\times10^{-5}$
X-ray Bgd. (c s-1 keV-1 pixel-1)	$\sim 2\times10^{-5}$	$\sim 6\times10^{-5}$	$\sim 8 \times 10^{-5}$	$\sim 3 \times 10^{-3}$

 

The OXS concept separates the processes of energy dispersion and imaging. The mosaic panel acts as a narrow bandpass filter and as a mirror. Each pixel in the reflected field of view of the telescope satisfies a specific Bragg angle on the crystal and, therefore, each pixel in the detector can be identified with a particular energy. Scans which involve repositioning of the telescope axis and the angle between the crystal panel and the telescope axis ( $45^{\circ}\pm15^{\circ}$) yield either the spectrum of a point source or energy resolved images of an extended source (Figure 56).