The X-Ray Telescope onboard Suzaku

TLDR

The Suzaku XRT achieves a half‑power diameter of 1.8′–2.3′, markedly better than the 3.6′ of the ASCA XRT. The study presents the design parameters, production process, and in‑flight performance of Suzaku’s X‑ray telescope. The XRT modules incorporate a pre‑collimator that suppresses stray light from 20′ and 50′ off‑axis directions, and the telescope’s design and manufacturing were optimized to meet these performance goals. The XRT’s optical axes lie within 1.3′, yielding >97 % observation efficiency, its vignetting matches ray‑tracing predictions within ~10 %, and Crab Nebula flux measurements agree with historical values within ~2 %.

Abstract

Abstract We present the design parameters, production process, and in-flight performance of the X-ray telescope (XRT) onboard Suzaku. The imaging capability is significantly improved over the ASCA XRT, which had half-power diameters of ${3\rlap {.}{}^{\mathrm {\prime }}6}$, to ${1\rlap {.}{}^{\mathrm {\prime }}8}$–${2\rlap {.}{}^{\mathrm {\prime }}3}$ for all four XRT-I modules. The optical axes are found to be distributed within a radius of ${1\rlap {.}{}^{\mathrm {\prime }}3}$, which makes the observation efficiency of all the XRTs more than 97% at the XIS-default observing position. The vignetting over the XIS field of view predicted via ray-tracing coincides with that measured for observations of the Crab Nebula to within $\sim 10\%$. Contemporaneous fits of a power law to all of the XIS spectra of the Crab Nebula taken at the two standard observing positions (XIS/HXD-default positions) gives a flux consistent with that obtained by Toor and Seward (1974, AJ, 79, 995) to within $\sim 2\%$. The pre-collimator on the top of each XRT module successfully reduces the intensity of the stray light from the $20'$ and $50'$-off directions down to the level of pre-flight expectations.