The Wide Field Imager instrument for Athena

Abstract

ESA's next large X-ray mission ATHENA is designed to address the Cosmic Vision science theme 'The Hot and Energetic Universe'. It will provide answers to the two key astrophysical questions how does ordinary matter assemble into the large-scale structures we see today and how do black holes grow and shape the Universe. The ATHENA spacecraft will be equipped with two focal plane cameras, a Wide Field Imager (WFI) and an X-ray Integral Field Unit (X-IFU). The WFI instrument is optimized for state-of-The-Art resolution spectroscopy over a large field of view of 40 amin x 40 amin and high count rates up to and beyond 1 Crab source intensity. The cryogenic X-IFU camera is designed for high-spectral resolution imaging. Both cameras share alternately a mirror system based on silicon pore optics with a focal length of 12 m and large effective area of about 2 m2at an energy of 1 keV. Although the mission is still in phase A, i.e. studying the feasibility and developing the necessary technology, the definition and development of the instrumentation made already significant progress. The herein described WFI focal plane camera covers the energy band from 0.2 keV to 15 keV with 450 μm thick fully depleted back-illuminated silicon active pixel sensors of DEPFET type. The spatial resolution will be provided by one million pixels, each with a size of 130 μm x 130 μm. The time resolution requirement for the WFI large detector array is 5 ms and for the WFI fast detector 80 μs. The large effective area of the mirror system will be completed by a high quantum efficiency above 90% for medium and higher energies. The status of the various WFI subsystems to achieve this performance will be described and recent changes will be explained here

The Physics of Galaxy Cluster Outskirts

“…ATHENA also features a wide field X-ray imager (WFI), with a field of view of 40×40 arcmin (Meidinger et al 2017). The combination of a large field of view and unprecedented effective area will allow the outskirts of clusters to be routinely unlocked for X-ray spectroscopy, allowing temperature and entropy measurements out to the virial radius and beyond for large samples of clusters.…”

ATHENA WFI optical blocking filters development status toward the end of the instrument phase-A

“…Figure 8 shows pictures of sample #3 partially representative of the LDA OBF, #4 fully representative of one quadrant of the LDA OBF, and #5 representative of the FDA OBF in the meshless option (not the baseline). Preliminary results have been reported elsewhere on optical characterization and surface analysis investigations [28], on vibration tests performed on the large size sample #3 at the Centre Spatial de Liege in March 2017, and on acoustic tests performed at the AGH University in Krakow in May 2017 [8]. Here we report some results from further optical characterization measurements and mechanical tests performed on new filter samples.…”

“…Athena, whose launch is scheduled around 2030, will be equipped with a 12 m focal length 10°1 0-2 10 grazing incidence X-ray telescope based on the innovative Silicon Pore Optics technology, capable to provide 1.4 m 2 effective area at 1 keV with an angular resolution of 5 arcsec full width at half maximum (FWHM) over a large field of view (> 40 arcmin diameter) [3] [4]. The telescope will be mounted on a moveable platform which will allow both focus adjustment and tilt to point the X-ray beam on one of the two focal plane instruments: the X-Ray Integral Field Unit (X-IFU) [5] [6], an array of micro-calorimeters, and the Wide Field Imager (WFI), a large array of depleted field effect transistors (DEPFET) pixels [7] [8].…”

“…With such time resolution, and operating out of focus by about 3.5 cm, the FDA will be able to detect bright point sources with an intensity of 1 Crab (approx. 110,000 counts per second), a throughput better than 80% and less than 1% pile-up [8]. The detector time resolution does not allow to use efficiently an anticoincidence technique to reject particle background, therefore, particular care is put in the design of passive shielding of particle induced background in order to achieve the scientific requirement of a value < 5  10 -3 cts/cm 2 /s/keV in the energy band between 2 keV and 7 keV for 60% of the time [9].…”

ATHENA X-IFU thermal filters development status toward the end of the instrument phase-A

“…ATHENA, whose launch is scheduled before 2030, will be equipped with a 12 m focal length grazing incidence X-ray telescope based on the innovative silicon pore optics technology, capable to provide 1.4 m 2 effective area at 1 keV with an angular resolution full width at half maximum (FWHM) of 5" over a large field of view (> 40' diameter) [3] [4]. The telescope will be mounted on a moveable platform which will allow both focus adjustment and tilt to point the X-ray beam on one of the two focal plane detectors: the X-ray Integral Field Unit (X-IFU) [5] [6] microcalorimeter array, and the large Wide Field Imager (WFI) [7] [8] depleted field effect transistors (DEPFET) array.…”