Hans M. Günther

An x-ray transmission grating spectrometer for Lynx

Hans M. Günther, Ralf Heilmann

SPIE 10699-39 (2017)


  • Plenty of X-ray observations require high-res spectroscopy, e.g.
    • temperature and density sensitive line ratios
    • narrow line WHIM absorption
    • resolve kinematic profile of wind emission lines
    • ...
  • Microcalorimeters are good at high energies
  • Grating spectroscopy is better at low energies
  • Lynx PSF + advanced gratings: > 10 times Chandra resolution
  • Lynx mirror + advanced gratings: up to 1000 times Chandra area at O VII

Simulation input

  • MARXS ray-trace code (Günther et al, ApJ, 2017):
    • Freely available at https://github.com/Chandra-MARX/marxs/
    • Hundreds of unit tests
    • Tested against lab data and Chandra observations
    • Written in Python
  • Data:
    • Mirror PSF: Assuming 0.5 arcsec half-power diameter
    • Critical angle transmission gratings (CAT), etched from Si. Using predicted efficiencies for 5.7 micron deep gratings.
    • Various filter curves, CCD QEs etc.

Size of grating facets

  • Small grating facets follow the Rowland torus well, but more area is lost for mounting structures, also number goes up.
  • Large gratings use the space better, but diverge from the ideal form more.

Can we have our cake and eat it, too?

The simple approach: Rectangular gratings


Can we have our cake and eat it, too?

Preserving the blaze: Bend gratings

FluxperCCD FluxperCCD

Can we have our cake and eat it, too?

Recovering the resolution: Chirped gratings

  • projection lithography masks can be written in any pattern
  • CAT grating production process with projection lithography is used for ARCUS
  • talk to Ralf Heilmann

Trade off resolving power and effective area

Can we have our cake and eat it, too?

ChandraX ChandraX

CCD placement

Detector placement

Effective area and resolving power

Aeff R

High-energy photons pass right through

Detector placement


  • CAT gratings can deliver the R, Aeff required by the Lynx science with (mostly) todays technology
  • Alignment tolerances are very forgiving
  • Trades and options:
    • Chirped gratings
    • Two traces
    • Grating coating