Guenther Kettenring

Description and performance of the low-energy transmission grating spectrometer on board Chandra

The Chandra spacecraft has been launched successfully on July 23, 1999. The payload consists of a high resolution X- ray telescope, two imaging detector systems in the focal plane and two transmission gratings. Each one of the two gratings can be put in the beam behind the telescope and the grating spectrometers are optimized for high and low energy, respectively. The Low Energy Transmission Grating Spectrometer consists of three parts: the high-resolution telescope, the transmission grating array and the detector, to read-out the spectral image.

The Rosat mission

The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 105) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets.The X-ray telescope consists of a fourfold nested Wolter type I mirror system with 80 cm aperture and 240 cm focal length, and three focal plane detectors. In the baseline version these will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 20 × 20.

Concept of the ROSITA X-ray camera

The main scientific objective of the ROSITA mission is to extend the X-ray all-sky survey of ROSAT to higher energies to gain an unbiased sample of all types of celestial X-ray sources in the medium energy band. During this mission the whole sky will be scanned by seven imaging X-ray telescopes. The telescopes have different viewing directions with an offset angle between 4 and 6 deg. The focal plane instrumentation of the telescopes is based on a novel type of pn-CCD with a frame store, an advanced version of the pn-CC operating quite successfully on XMM-Newton. The pixel size is adapted to the mirror resolution and the fast readout time guaranties the required angular accuracy despite the scan motion. The X-ray camera carries seven separate CCDs arranged on a circle in the foci of the Wolter type I mirror systems of the seven telescopes. The CCDs are mounted on ceramic frames, which carry dedicated front-end electronics for each CCD. The CCDs are operated at a temperature of-80 deg C. Except for the entrance window, the CCDs are covered by graded shielding for suppression of fluorescent X-ray background, generated by cosmic rays in the surrounding materials. Filters in front of the the CCDs, inhibit optical and UV photons. For in-orbit calibration a radioactive source producing fluorescent X-rays in the desired energy band is provided. We will give an overview of the mechanical, thermal and electrical concept of the camera system.

FIFI LS: a field-imaging far-infrared line spectrometer for SOFIA

We describe our design for an imaging far-IR spectrometer for NASA/DARAs SOFIA observatory. The design of the instrument is driven by the goal of maximizing observing efficiency. Since the sensitivity of well designed FIR instruments is limited by the thermal background of telescope and atmosphere, observing efficiency can only be increased by increasing the throughput of the spectrometer and the number of simultaneous data channels. Our instrument will feature two separate medium resolution grating spectrometers with common fore-optics feeding two large Ge:Ga arrays. The two Littrow spectrometers operate between 45-110 micrometers , and 110-210 micrometers , resp., in 1st and 2nd order. Multiplexing takes place both spectrally and spatially. An image slicer redistributes 5 by 5 pixel fields-of-view along the 1 by 25 pixel entrance slits of the spectrometers. Anamorphic collimator mirrors help keep the spectrometer compact in the cross-dispersion direction. The spectrally dispersed images of the flits are anamorphically projected onto the detector arrays, to independently match spectral and spatial resolution to detector size. We will thus be able to instantaneously cover a velocity range of approximately 1500 km/s around a selected FIR spectral line, for each of the 25 spatial pixels. For calibration and flatfielding we use blackbody calibrators internal to the instrument, at signal levels comparable to the thermal background of the telescope. An image rotator compensates field rotation during long integrations. Estimated sensitivity of the spectrometer is approximately 2 by 10-15W/(root)Hz/pixel.