An x-ray transmission grating spectrometer for Lynx

SPIE 10699-39 (2017)

Motivation

• 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

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?

CCD placement

Effective area and resolving power

High-energy photons pass right through

Summary

• 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