The Wide Field Imager of the International X-ray Observatory

Space Research Centre, Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (Impact Factor: 1.32). 12/2010; DOI: 10.1016/j.nima.2010.05.049
Source: OAI

ABSTRACT The International X-ray Observatory (IXO) will be a joint X-ray observatory mission by ESA, NASA and JAXA. It will have a large effective area (3 m2 at 1.25 keV) grazing incidence mirror system with good angular resolution (5 arcsec at 0.1–10 keV) and will feature a comprehensive suite of scientific instruments: an X-ray Microcalorimeter Spectrometer, a High Time Resolution Spectrometer, an X-ray Polarimeter, an X-ray Grating Spectrometer, a Hard X-ray Imager and a Wide-Field Imager.The Wide Field Imager (WFI) has a field-of-view of 18 ft×18 ft. It will be sensitive between 0.1 and 15 keV, offer the full angular resolution of the mirrors and good energy resolution. The WFI will be implemented as a 6 in. wafer-scale monolithical array of 1024×1024 pixels of size. The DEpleted P-channel Field-Effect Transistors (DEPFET) forming the individual pixels are devices combining the functionalities of both detector and amplifier. Signal electrons are collected in a potential well below the transistor's gate, modulating the transistor current. Even when the device is powered off, the signal charge is collected and kept in the potential well below the gate until it is explicitly cleared. This makes flexible and fast readout modes possible.

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    ABSTRACT: The ROOT based Offline and Online Analysis (ROAn) framework was developed to perform data analysis on data from Depleted P-channel Field Effect Transistor (DePFET) detectors, a type of active pixel sensors developed at the MPI Halbleiterlabor (HLL). ROAn is highly flexible and extensible, thanks to ROOT׳s features like run-time type information and reflection. ROAn provides an analysis program which allows to perform configurable step-by-step analysis on arbitrary data, an associated suite of algorithms focused on DePFET data analysis, and a viewer program for displaying and processing online or offline detector data streams. The analysis program encapsulates the applied algorithms in objects called steps which produce analysis results. The dependency between results and thus the order of calculation is resolved automatically by the program. To optimize algorithms for studying detector effects, analysis parameters are often changed. Such changes of input parameters are detected in subsequent analysis runs and only the necessary recalculations are triggered. This saves time and simultaneously keeps the results consistent. The viewer program offers a configurable Graphical User Interface (GUI) and process chain, which allows the user to adapt the program to different tasks such as offline viewing of file data, online monitoring of running detector systems, or performing online data analysis (histogramming, calibration, etc.). Because of its modular design, ROAn can be extended easily, e.g. be adapted to new detector types and analysis processes.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 10/2014; 762:142–148. · 1.32 Impact Factor
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    ABSTRACT: To improve the signal to noise level, devices for optical and x-ray astronomy use techniques to suppress background events. Well known examples are e.g. shutters or frame-store Charge Coupled Devices (CCDs). Based on the DEpleted P-channel Field Effect Transistor (DEPFET) principle a so-called Gatebale DEPFET detector can be built. Those devices combine the DEPFET principle with a fast built-in electronic shutter usable for optical and x-ray applications. The DEPFET itself is the basic cell of an active pixel sensor build on a fully depleted bulk. It combines internal amplification, readout on demand, analog storage of the signal charge and a low readout noise with full sensitivity over the whole bulk thickness. A Gatebale DEPFET has all these benefits and obviates the need for an external shutter. Two concepts of Gatebale DEPFET layouts providing a built-in shutter will be introduced. Furthermore proof of principle measurements for both concepts are presented. Using recently produced prototypes a shielding of the collection anode up to 1 • 10-4 was achieved. Predicted by simulations, an optimized geometry should result in values of 1 • 10-5 and better. With the switching electronic currently in use a timing evaluation of the shutter opening and closing resulted in rise and fall times of 100ns.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2012; · 0.20 Impact Factor
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    ABSTRACT: Soft protons can be a major source of degradation of the performances of instrumentation in space, in particular for CCDs. It was learned from the experience of Chandra and XMM-Newton that they can be funneled through the mirrorshells of an X-ray telescope down to the focal plane and hit detectors. This seems the favoured mechanism, since in general a detector placed at the focal plane is completely shielded from environmental soft protons except that in correspondance of the aperture field of view. However, the bombardment of high-energy cosmic rays can induce spallation reactions in the shield itself and other materials present at the focal plane. These processes generate secondary hadrons at softer energy, which can escape the target and reach the detectors. The products of spallation are mainly protons and neutrons. Neutrons can also have an impact on the performances of a Silicon-based detector. We study the production of secondary hadrons in the case of the pn-CCDs aboard eROSITA and the DEPFET Wide Field Imager aboard ATHENA, calculate expected doses over the missions duration and discuss possible effects on these detectors.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; · 0.20 Impact Factor

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