Spectroscopic performance of flight-like DEPFET sensors for Athena's WFI

Abstract

The Wide Field Imager for the Athena X-ray telescope is composed of two back side illuminated detectors using DEPFET sensors operated in rolling shutter readout mode: A large detector array featuring four sensors with 512x512 pixels each and a small detector that facilitates the high count rate capability of the WFI for the investigation of bright, point-like sources. Both sensors were fabricated in full size featuring the pixel layout, fabrication technology and readout mode chosen in a preceding prototyping phase. We present the spectroscopic performance of these flight-like detectors for different photon energies in the relevant part of the targeted energy range from 0.2 keV to 15 keV with respect to the timing requirements of the instrument. For 5.9 keV photons generated by an iron-55 source the spectral performance expressed as Full Width at Half Maximum of the emission peak in the spectrum is 126.0 eV for the Large Detector and 129.1 eV for the Fast Detector. A preliminary analysis of the camera's signal chain also allows for a first prediction of the performance in space at the end of the nominal operation phase.