Objective Crystal Spectrometer on the SRG satellite

The flight version of the Objective Crystal Spectrometer (OXS) on the SPECTRUM-X- GAMMA satellite is presented. The spectrometer is a panel that is placed in front of one of the SODART telescopes. It is composed of an array of the three Bragg crystals, LiF(220), Si(111) and RAP(001) for high resolution spectroscopy in the energy bands that encompass the H- and He-like emission line features from the cosmically important elements Fe, S, Ar and O. An energy resolution (E/(Delta) E) of 1250 will be obtained for He-like Fe emission, > 3000 for He-like S and Ar, > 700 for He-like O. In addition, the Si crystals will be coated with a multilayer that will allow spectroscopy with an energy resolution of approximately 80 in the energy band immediately below the C-K absorption edge of 0.284 keV. All the flight crystals are available and detailed calibrations have been obtained for each crystal. They confirm our specifications for the overall performance of the OXS. An estimate of the effective area in the 4 energy windows that are available to OXS yields > 100 cm² from 5 to 7.4 keV, > 200 cm² from 2.3 to 4.6 keV, approximately 10 cm+2) from 0.55 to 0.81 keV and approximately 100 cm² from 0.175 to 0.28 keV.