Filters design and characterization for LAD instrument onboard eXTP

Abstract

The LAD (Large Area Detector) instrument, onboard the Sino-European mission eXTP (enhanced X-ray Timing and Polarimetry), will perform single-photon, high-resolution timing and energy measurements, in the energy range 2–30 keV, with a large collecting area. Its silicon drift detectors need shielding from NIR/Vis/UV light by astrophysical sources and the bright Earth, to avoid performance degradation. Filters made of an Al coated thin polyimide (PI) membrane will guarantee the needed out-of-band rejection while offering high X-ray transparency. They will be placed between the detectors and the capillary plate plate collimators, open to the external environment. The mission is now in phase B2 and a baseline design for the filters was produced. We describe the filter design and modeling activity, and report the characterization performed so far on X-ray transmission, pinhole and defects, thermo-vacuum cycling endurance, and bright Earth optical load shielding properties.