Low Energy Modular Array (LEMA)

LEMA operates in the 0.2-12 keV band, employing an aligned collection of 60 X-ray concentrator optics (XRCs) and COTS silicon drift detectors (SDDs) that provide over 8.5x the collecting area of NICER (on the International Space Station, the heritage instrument for LEMA). In addition to the increased collecting area, LEMA has a substantially reduced, and more stable, background.

Instrument Details

Low background, low cost, light weight single bounce foil concentrators developed for NICER. Much simpler and cheaper than traditional X-ray optics. Focal length 3 m with 2’ focal spots for enhanced throughput >2.5 keV (relative to NICER).

  • 60 X-ray Concentrator units
  • Energy range: 0.2-12 keV
  • Energy resolution: 85-175 eV FWHM
  • Effective area @1.5 keV: 1.6 m2 (>8.5× NICER)
  • Time resolution: 100 ns

The heart of LEMA are the X-ray concentrators that GSFC has optimized over years of manufacturing across multiple programs. The image shows 56 concentrators installed in the NICER optical bench. For LEMA, the X-ray concentrator and detector pairs are mounted to a composite optical bench which is manufactured from low Coefficient of Thermal Expansion materials, providing a stable foundation across the wide range of Sun angles and orbital conditions. Our partners from Ball Aerospace will provide the optical bench and have decades long experience in the design, analysis and manufacturing of such hardware, most recently on the Roman Space Telescope.

For LEMA, the X-ray concentrator optics will be enlarged relative to those used in NICER, with 107 nested foil shells with diameters between 3 and 28 cm. The focal length is also extended to 3 m. In the image, a NICER optic is on the right and a larger optic, similar to what will be used for LEMA is on the left.

LEMA uses commerical Amptek silicon drift detectors that have been flight proven on NICER (shown with and without the hermetically-sealed cap). The readout electronics in the FPM have only minor modifications from what is currently operating on NICER.