X-ray Astronomy Imaging Research Articles

Development of a microcalorimeter array for wide energy band X-ray astronomy

Some experience has been acquired by the CEA/DSM/DAPNIA/SAp in IR bolometer arrays realization in collaboration with the LETI (Grenoble). From this basis, we are undertaking a development of an X-ray sensitive array for X-ray astronomy imaging spectroscopy missions. We are conservative in using only standard and well-known silicon processing technologies. An implanted and diffused silicon MESA structure is used, in place of ionic multi-implanted silicon, to provide the thermal sensor. Using this technology, we expect to obtain a set of homogeneous sensor of high volume, and low noise. The absorber will be a high Z material. HgTe is a candidate, high Z superconducting alternatives are explored. The absorber is hybridized, with indium beads providing a thermomechanical coupling, to the sensor plate. The microcalorimeter is decoupled from the cold sink by narrow silicon beams, following the structure already used for the IR arrays. The extrapolation of the X-ray thermal sensor is presently being pursued. Measurements of the characteristics of the sensors of the last batch of array prototypes are presented. With this standard silicon technology, we expect to obtain a low spread in sensor parameters, as is required by a multiplexed readout scheme.

Novel pixel detectors for X-ray astronomy and other applications

Following previous work in particle physics, the MPI Semiconductor Laboratory has been founded with the purpose of developing novel semiconductor detectors for particle physics and X-ray astronomy. A short description of the already successfully concluded development of pn-CCDs for focal imaging in X-ray astronomy (XMM/Newton X-ray Observatory) is given and the much more demanding requirements in a future X-ray astronomy experiment (XEUS) are discussed. A new type of pixel detector is proposed which will be capable to meet these requirements. It is based on the “DEPleted-Field Effect Transistor (DEPFET)” principle. The device operated on a fully depleted silicon wafer allows an internal charge amplification directly above the position where the signal conversion takes place. A very low gate capacitance of the DEPMOS transistor leads to low noise amplification. In contrast to CCDs, neither transfer loss nor “out-of-time events” can occur in a DEPFET-array. A very interesting feature is the possibility of repeated non-destructive readout which can be used for noise reduction even for the low-frequency (1/ f) noise. This type of detector will also have its applications in linear collider experiments.

X-Ray Studies of Clusters of Galaxies with The Einstein Observatory

With the advent of imaging in X-ray astronomy, we can, for the first time, study extended sources with the same detailed spatial and spectral resolution employed by radio and optical astronomers. As in other fields of astronomy, the study of the X-ray emission from clusters of galaxies is beginning to feel the tremendous impact of this advance. The accompanying contributions by Murray and by Grindlay show that the division of clusters into classes based solely on X-ray morphology holds clear implications for the origin of the intracluster medium and the evolution of the cluster as a whole. Comparisons with optical and radio data, along with detailed X-ray studies of nearby objects and the extension of cluster observations to redshifts greater than 0.5, will help connect these ideas to a sound theoretical base. In this report on the cluster observations performed by the Columbia Astrophysics Laboratory with the Einstein Observatory, we restrict ourselves to three brief comments concerning the following areas: (1) The correlation of X-ray brightness with cluster morphology, (2) the detection of a spiral-rich cluster at z ˜ 0.4, and (3) detailed observations of Coma, the nearest rich cluster.

The Skylab X-Ray Spectroheliograph

On May 14, 1973, Skylab was placed in earth orbit by the National Aeronautics and Space Administration. The major scientific payload of this experimental space station is the Apollo Telescope Mount (ATM) which houses six major telescope instruments. As a group, these instruments are capable of observing the sun's radiation from X-rays to visible light. The Skylab program consists of three manned observing periods; the first period having a twenty-eight day duration, the second and third each having fifty-six days duration. These three observing periods are separated by unmanned periods of approximately forty days duration. From the data collected in these three observing periods, solar physicists will try to answer some of the basic questions concerning solar flares, solar activity, the heating of the solar corona and the solar cycle. The purpose of this paper is to give a brief description of the hardware and performance of one of these instruments, the X-ray spectroheliograph. The conceptual design of this instrument and scientific details of the subsystems have been discussed in Reference 2 as part of a general discussion on "Imaging in X-Ray Astronomy". A more extensive presentation of the instrument as a whole in the context of the goals in the solar physics area is in preparation (Reference 3).