Performance Testing of a Large-Format X-ray Reflection Grating Prototype for a Suborbital Rocket Payload

The soft X-ray grating spectrometer on board the Off-plane Grating Rocket Experiment (OGRE) hopes to achieve the highest resolution soft X-ray spectrum of an astrophysical object when it is launched via suborbital rocket. Paramount to the success of the spectrometer are the performance of the >250 reflection gratings populating its reflection grating assembly. To test current grating fabrication capabilities, a grating prototype for the payload was fabricated via electron-beam lithography at The Pennsylvania State University's Materials Research Institute and was subsequently tested for performance at Max Planck Institute for Extraterrestrial Physics' PANTER X-ray Test Facility. Bayesian modeling of the resulting data via Markov chain Monte Carlo (MCMC) sampling indicated that the grating achieved the OGRE single-grating resolution requirement of Rg(λ/λ)>4500 at the 94% confidence level. The resulting Rg posterior probability distribution suggests that this confidence level is likely a conservative estimate though, since only a finite Rg parameter space was sampled and the model could not constrain the upper bound of Rg to less than infinity. Raytrace simulations of the tested system found that the observed data can be reproduced with a grating performing at Rg=∞. It is therefore postulated that the behavior of the obtained Rg posterior probability distribution can be explained by a finite measurement limit of the system and not a finite limit on Rg. Implications of these results and improvements to the test setup are discussed.