X-ray performance of critical-angle transmission grating prototypes for the Arcus mission

Kavli Affiliate: Mark L. Schattenburg

| First 5 Authors: Ralf K. Heilmann, Alexander R. Bruccoleri, Vadim Burwitz, Casey deRoo, Alan Garner

| Summary:

Arcus is a proposed soft x-ray grating spectrometer Explorer. It aims to
explore cosmic feedback by mapping hot gases within and between galaxies and
galaxy clusters and characterizing jets and winds from supermassive black
holes, and to investigate the dynamics of protoplanetary discs and stellar
accretion. Arcus features 12 m-focal-length grazing-incidence silicon pore
optics (SPO) developed for the Athena mission. Critical-angle transmission
(CAT) gratings efficiently disperse high diffraction orders onto CCDs. We
report new and improved x-ray performance results for Arcus-like CAT gratings,
including record resolving power for two co-aligned CAT gratings. Multiple
Arcus prototype grating facets were illuminated by an SPO at the PANTER
facility. The facets consist of $32times32.5$ mm$^2$ patterned silicon
membranes, bonded to metal frames. The bonding angle is adjusted according to
the measured average tilt angle of the grating bars in the membrane. Two
simultaneously illuminated facets show minor broadening of the Al-K$_{alpha}$
doublet in 18$^{rm th}$ and 21$^{rm st}$ orders with a best fit record
effective resolving power of $R_G approx 1.3^{+infty}_{-0.5}times10^4$
($3sigma$), about 3-4 times the Arcus requirement. We measured the diffraction
efficiency of quasi-fully illuminated gratings at O-K wavelengths in orders 4-7
in an Arcus-like configuration and compare results with synchrotron spot
measurements. After corrections for geometrical effects and bremsstrahlung
continuum we find agreement between full and spot illumination at the two
different facilities, as well as with the models used for Arcus effective area
predictions. We find that these flight-like gratings meet diffraction
efficiency and greatly exceed resolving power Arcus requirements.

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