Adam N. Brunton

LOBSTER-ISS: an imaging x-ray all-sky monitor for the International Space Station

We describe the design of Lobster-ISS, an X-ray imaging all-sky monitor (ASM) to be flown as an attached payload on the International Space Station. Lobster-ISS is the subject of an ESA Phase-A study which will begin in December 2001. With an instantaneous field of view 162 x 22.5 degrees, Lobster-ISS will map almost the complete sky every 90 minute ISS orbit, generating a confusion-limited catalogue of ~250,000 sources every 2 months. Lobster-ISS will use focusing microchannel plate optics and imaging gas proportional micro-well detectors; work is currently underway to improve the MCP optics and to develop proportional counter windows with enhanced transmission and negligible rates of gas leakage, thus improving instrument throughput and reducing mass. Lobster-ISS provides an order of magnitude improvement in the sensitivity of X-ray ASMs, and will, for the first time, provide continuous monitoring of the sky in the soft X-ray region (0.1-3.5 keV). Lobster-ISS provides long term monitoring of all classes of variable X-ray source, and an essential alert facility, with rapid detection of transient X-ray sources such as Gamma-Ray Burst afterglows being relayed to contemporary pointed X-ray observatories. The mission, with a nominal lifetime of 3 years, is scheduled for launch on the Shuttle c.2009.

AXAF High-Resolution Camera (HRC): calibration and recalibration at XRCF and beyond

The high resolution camera (HRC) is a microchannel plate based imaging detector for the Advanced X-Ray Astrophysics Facility (AXAF) that will be placed in a high earth orbit scheduled for launch in August, 1998. An end-to-end calibration of the HRC and the AXAF high resolution mirror assembly (HRMA) was carried out at the Marshall Space Flight Centers X-Ray Calibration Facility (XRCF). This activity was followed by several modifications to the HRC to improve its performance, and a series of flat field calibrations. In this paper, and the following companion papers, we discuss the calibration plans, sequences, and results of these tests. At the time of this conference, the HRC has been fully flight qualified and is being integrated into the science instrument module (SIM) in preparation for integration into the AXAF spacecraft.

X-ray focusing using square-pore microchannel plates First observation of cruxiform image structure

Abstract Soft X-ray (0.28 and 1.74 keV) images produced by the focusing action of a planar, square-pore microchannel plate (MCP) are described. These images contain for the first time the three-component cruxiform structure expected from the studies of Angel [Astrophys. J. 233 (1979) 364] and Chapman et al. [Rev. Sci. Instr. 62 (1991) 1542], and so indicate a high degree of geometric regularity within and between the ∼ 46000 active channels in the MCP structure. The angular resolution of the central “true” focus is ∼ 10 arc min FWHM.

X-ray focusing with Wolter microchannel plate optics

Abstract Square-pore microchannel plate (MCP) X-ray optics of the “lobster-eye” geometry have frequently been described in the literature. We have now investigated the use of a radial channel packing geometry which, in the context of an MCP pair slumped to the correct radii of curvature, can form a conic approximation to the Wolter Type I grazing incidence X-ray optic. Such an optic can provide a large effective area with very low mass and may be ideally suited for use in applications such as planetary imaging X-ray fluorescence. We present here the results of X-ray illumination of the first such optic, fabricated by Photonis SAS, France.

Microchannel-plate-based x-ray optics

X-ray optics based on micro-channel plates (MCPs) offer some distinctive advantages over conventional technologies used to produce imagin optics for astrophysics applications. Such micro-pore optics (MPOs) are far lighter and allow a larger stacking density than optics based on metallic foils or plates. Until recent, x-ray optics based on MCPs were not feasible or useful because of the limited quality of the MCPs. We have produced thick square pore MPOs of improved quality and have developed methods to stack the channels in a radial pattern, as required for imagin optics based on Wolter type I or II designs. The individual plates were tested in synchrotron radiation facilities and conventional beam lines to determine their geometric and surface scattering properties.

PRODUCTION OF QUASI-PARALLEL X-RAY-BEAMS USING MICROCHANNEL PLATE X-RAY LENSES

Abstract We describe the soft X-ray (0.28 and 1.74 keV) images produced by a spherically-slumped microchannel plate (MCP) optic with a nominal radius of curvature, R, of 1.4 m. With a pointlike X-ray source situated at the focus, an axial distance R 2 from the MCP on the concave side, this structure produces, in the manner of a lens, a quasi-parallel output beam whose energy-dependent intensity profile corresponds closely to the predictions of (i) a simple 1D analytical model and (ii) a 2D Monte Carlo ray-trace code. With the source on the convex side of the slumped plate, we observe X-ray focusing which is again consistent with our models. Analysis of the X-ray image structure observed in focusing mode yields an upper limit to the rms surface roughness of the lead glass channel walls of 50 A.

A study of 8.5 mu m microchannel plate X-ray optics

Abstract We have investigated the X-ray focusing properties of microchannel plates (MCPs) with square channels of side length 8.5 μ m. Both planar and spherically slumped MCPs (radius of curvature R slump =0.5m) have been examined. We have observed foci of 7 ′ and 14 ′ FWHM, respectively. In addition, we have measured the 8 keV X-ray reflectivity of channel surfaces which have been subjected to a variety of chemical treatments. These reflectivities are found to correspond closely to theoretical values calculated by a simple two-layer model of the MCP reflecting surfaces. The inferred values of surface roughness for those MCPs thermally annealed at 430°C is ∼11 A, about a factor of two better than previously measured.

Recent studies of lobster-eye optics

Lobster-eye optics have been proposed as an exciting development in the field of x-ray all-sky monitors. However, to date their potential has mainly been analyzed in the context of an all-sky monitor for a small satellite mission. We examine the wide range of parameters available for lobster-eye optics with different configurations. The sensitivity of the various schemes is calculated. We have also examined the current state of the art in actual lobster-eye optics. We present our experimental results and discuss realistic targets for manufacture. The impact of these targets on the calculated sensitivities is also described.

In-flight Performance and Calibration of the Chandra High Resolution Camera Imager (HRC-I)

In this paper we present and compare flight results with the latest results of the ground calibration for the HRC-I detector. In particular we will compare ground and in flight data on detector background, effective area, quantum efficiency and point spread response function.

Performance and calibration of the AXAF High-Resolution Camera II: the spectroscopic detector

The high resolution camera (HRC) is one of two focal plane detector systems that will be flown on the Advanced X-ray Astrophysics Facility (AXAF). The HRC consists of two microchannel plate (MCP) detectors: one to provide large area, high position resolution imaging and timing (HRC-I), and a second (HRC-S) to provide a readout for the AXAF low energy transmission gratings. Each detector is composed of a chevron pair of CsI coated MCPs with a crossed grid charge detector and an Al/polyimide UV/ion shield. In this paper, we describe the operation, performance and calibration of the spectroscopic detector. In particular, we discuss the absolute quantum efficiency calibration, the point spread function of the instrument combined with the AXAF telescope, the count rate linearity, the spatial linearity, and the internal background of the instrument. Data taken in the laboratory and at the x-ray Calibration Facility at Marshall Space Flight Center are presented.