Suzaku XRT

X-Ray Telescopes (XRTs)

Suzaku carries five X-ray telescopes; four identical units for the four XISs (XRT-I) and the fifth for the XRS (XRT-S). They consist of nested conical thin-foil mirrors which share similar design concepts with ASCA XRT (Serlemitsos et al. 1995, PASJ, 47, 105), but with several improvements. In table 1, characteristics of ASCA and Suzaku XRTs are compared. The weight of each mirror unit is about 20 kg both for XRT-I and XRT-S. Each unit consists of two stages (primary and secondary), and each stage is divided into four quadrants. For XRT-I, each quadrant of each stage carries 175 thin foils, while there are 168 foils per quadrant per stage of XRT-S. The radii of the outermost foils are 20.0 cm both for XRT-I and XRT-S. The focal length is 450 cm for XRT-S and 475 cm for XRT-I.

The half power-diameter (HPD) is about 1.9'. Compared to ASCA XRT, the ratio of the focal length over the diameter is larger, thereby incident angles of the X-rays to the mirror surface are smaller. This leads to better reflectivity in the high energy band above ~5 keV. The effective area per telescope is typically 440 cm² at 1.5 keV and 250 cm² at 8 keV.

Reflective surfaces of the thin foils are coated with gold.

	ASCA XRT	Suzaku XRT-S	Suzaku XRT-I
Number of Telescope	4	1	4
Diameter	345mm	400mm	399mm
Focal Length	3.5 m	4.5 m	4.75 m
No. of Foils to Nest	120	168	175
Production	Acrylic lacquer finish	Epoxy coupling layer	Epoxy coupling layer
Geometric area/telescope	558 cm²	887 cm²	873 cm²
Weight/telescope	9.84 kg	18.5 kg	19.5 kg

Table 1: Telescope Dimensions and Parameters of XRT

Pre-Collimator

The pre-collimator, which blocks off stray light, consists of nested aluminum foils similar to that of the refrector substrates but shorter. They are installed on top of their resspective primary reflectors.

Thermal Shields

If the telescope cools more rapidly than the satellite body, this could lead to the deformation of the telescope structure. Also the mirror surface could absorb out-gas from the satellite and its performance would then degrade. Therefore, a thermal shield is put on the top of each XRT to prevents heat from escaping through the telescope aperture into space. In addition, the thermal shield prevents oxygen atoms in orbit to bombard and damage the mirror surface. The XRT thermal shield is made of PET (C₁₀H₈O₄; Toray Lumirror, which is the same material as Dupont Mylar) coated with aluminum. The thickness of the PET and the aluminum coating are 0.2 micron and 0.03 micron, respectively, and their densities are 1.41 g cm^-3 and 2.69 g cm^-3. The thermal shield is supported by a stainless steel mesh structure whose thickness is 0.15 mm. The mesh does not transmit X-rays, and putting thermal shield reduce the geometrical effective area to 93.4 %.

For more information, please see the XRT page maintained by the GSFC XRT team.

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This file was last modified on Thursday, 18-May-2006 12:00:49 EDT