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Proceedings Paper

The wide field imager instrument for Athena
Author(s): Norbert Meidinger; Josef Eder; Tanja Eraerds; Kirpal Nandra; Daniel Pietschner; Markus Plattner; Arne Rau; Rafael Strecker
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Paper Abstract

The WFI (Wide Field Imager) instrument is planned to be one of two complementary focal plane cameras on ESA’s next X-ray observatory Athena. It combines unprecedented survey power through its large field of view of 40 amin x 40 amin together with excellent count rate capability (≥ 1 Crab). The energy resolution of the silicon sensor is state-of-the-art in the energy band of interest from 0.2 keV to 15 keV, e.g. the full width at half maximum of a line at 7 keV will be ≤ 170 eV until the end of the nominal mission phase. This performance is accomplished by using DEPFET active pixel sensors with a pixel size of 130 μm x 130 μm well suited to the on-axis angular resolution of 5 arcsec half energy width (HEW) of the mirror system. Each DEPFET pixel is a combined sensor-amplifier structure with a MOSFET integrated onto a fully depleted 450 μm thick silicon bulk. Two detectors are planned for the WFI instrument: A large-area detector comprising four sensors with a total of 1024 x 1024 pixels and a fast detector optimized for high count rate observations. This high count rate capable detector permits for bright point sources with an intensity of 1 Crab a throughput of more than 80% and a pile-up of less than 1%. The fast readout of the DEPFET pixel matrices is facilitated by an ASIC development, called VERITAS-2. Together with the Switcher-A, a control ASIC that allows for operation of the DEPFET in rolling shutter mode, these elements form the key components of the WFI detectors. The detectors are surrounded by a graded-Z shield, which has in particular the purpose to avoid fluorescence lines that would contribute to the instrument background. Together with ultra-thin coating of the sensor and particle identification by the detector itself, the particle induced background shall be minimized in order to achieve the scientific requirement of a total instrumental background value smaller than 5 x 10-3 cts/cm2/s/keV. Each detector has its dedicated detector electronics (DE) for supply and data acquisition. Due to the high frame rate in combination with the large pixel array, signal correction and event filtering have to be done on-board and in real-time as the raw data rate would by far exceed the feasible telemetry rate. The data streams are merged and compressed in the Instrument Control and Power distribution Unit (ICPU). The ICPU is the data, control and power interface of the WFI to the Athena spacecraft. The WFI instrument comprises in addition a filter wheel (FW) in front of the camera as well as an optical stray-light baffle. In the current phase A of the Athena project, the technology development is performed. At its end, breadboard models will be developed and tested to demonstrate a technical readiness level (TRL) of at least 5 for the various WFI subsystems before mission adoption in 2020.

Paper Details

Date Published: 18 July 2016
PDF: 12 pages
Proc. SPIE 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, 99052A (18 July 2016); doi: 10.1117/12.2231604
Show Author Affiliations
Norbert Meidinger, Max-Planck-Institut für extraterrestrische Physik (Germany)
Josef Eder, Max-Planck-Institut für extraterrestrische Physik (Germany)
Tanja Eraerds, Max-Planck-Institut für extraterrestrische Physik (Germany)
Kirpal Nandra, Max-Planck-Institut für extraterrestrische Physik (Germany)
Daniel Pietschner, Max-Planck-Institut für extraterrestrische Physik (Germany)
Markus Plattner, Max-Planck-Institut für extraterrestrische Physik (Germany)
Arne Rau, Max-Planck-Institut für extraterrestrische Physik (Germany)
Rafael Strecker, Max-Planck-Institut für extraterrestrische Physik (Germany)

Published in SPIE Proceedings Vol. 9905:
Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray
Jan-Willem A. den Herder; Tadayuki Takahashi; Marshall Bautz, Editor(s)

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