The Mercury Imaging X-ray Spectrometer (MIXS): Lessons learned for the ATHENA Wide Field Imager (WFI) GW Fraser, A Martindale and C Thomas Space Research Centre, Department of Physics and Astronomy, University of Leicester, UK On behalf of the BepiColombo MIXS Team 1. BepiColombo ESA/JAXA mission to Mercury, launch July,2016, arrival MIXS – first true imaging X-ray telescope for planetary XRF 3. Enabling technologies - low mass MCP optics and DEPFET arrays 4. DEPFET advantages include: radiation tolerance and high-temp operation 5. MIXS Flight Model delivery scheduled for Q3/ MIXS as a “pathfinder” for the Wide Field Imager?

BepiColombo Science Requirements for the mapping of the elemental composition of Mercury on global, intermediate and local scales dictate two complementary X-ray channels Wide field-of-view – Non-Imaging Collimator MIXS-C Narrow field-of-view – Imaging Telescope MIXS-T Common detector format – 64 x64 pixel, 300 x 300 micron DEPFET APS

QM MIXS

MIXS Functional Schematic MEB MIXS Electronics Box 1660 g FPA Focal Plane Assembly 1330g FEE Front End Electronics 248g DPA Detector Plane Array

Detector Assembly

MIXS Electronic Block Diagram

ATHENA WFI Electronic Block Diagram (Figure 6 of Rau et al.)

Athena WFI (central detector)BepiColombo MIXS-T and -C 256 x 256 DEPFET pixels64x64 DEPFET pixels 100 x 100 microns300 x300 microns Array divided north and south Operating Temp -40 degCOperating Temp -55 to +20 degC Gateable (27 bias voltages?)Non-Gateable (25 bias voltages) Maximum Rate (1 Crab equivalent) 350,000 events/s <150eV 6 keV140 eV

MIXS-C LM6 room temperature switch-on (not gain calibrated  3 peaks) Offset tracking Increase of energy with time at start of observation is caused by the MEB tracking the offsets to their operating level after switch on.

MIXS-C QM operating at room temperature Offset tracking Noisy pixel identified by OBSW and turned off Energy (arb.) Time ( arb. And non linear) Events per bin Noisy pixel identified by OBSW and turned off The noisy pixel in the QM is only visible at room temperature and is turned off by the OBSW after it is identified by autonomous algorithms

Gain, Offset and Noise

X-ray calibration of MIXS FM

Carbon and Oxygen band response

Titanium Self-fluorescence

Stainless steel target

Conclusions The BepiColombo MIXS DEPFET focal plane array provides a direct technical precursor, in FM build for an ESA Cornerstone mission, for the ATHENA WFI Sensor control, communication and internal calibration have been implemented in a rad-hard FPGA Split pixel, hot pixel.. Corrections have been implemented in OBSW Front End Electronics have been implemented in low-mass, hybrid components MIXS DEPFET detectors have been subjected to environmental test and detailed X-ray calibration and provide a basis for power and mass estimates for the WFI TRL 6 now