The SODART-OXS Bragg spectrometer of the SRG mission

• The SODART X-ray telescope includes an objective crystal spectrometer (OXS) in front of the mirrors in the optical block which provides an excellent energy resolution due to Bragg reflection. The picture shows SODART in the test hall.

• During a normal observation, the Bragg window (gray) on the left is closed (as here). The Bragg panel behind it is oriented parallel to the telescope axes. So the radiation can pass the telescope straightly through the front windows (silver), is collimated by the mirrors (middle silver holder), and reaches the focal plane square detector support structure (dark gray) at 8 m distance.

• During a Bragg observation the left front window is closed. The radiation enters through the open Bragg window, hits the inclined Bragg panel, and is reflected by the crystals towards the mirrors. By turning the panel in small angular steps, slightly different energies are filtered out of the spectrum.

• Parallel observations with one SODART telescope in Bragg source direction and theother one (and all other telescopes) in main direction are in principle possible. However, the possible angular distances of the sources to each other and to the Sun are strongly constrained. A software package to support parallel observation planning is available.

• Set-up: The spectrometer consists of a 63 cm diameter turnable flat panel covered on one side with 63 x 23 mm² size LiF(220) crystals, on the other with 60 x 60 mm² Si(111) and 60 x 20 mm² RAP(001) crystals. The superpolished Si crystal surfaces are coated with 70 C/Co layers forming an artificial crystal (ML) upon them.

• Status: The crystals had been individually measured and glued onto the Bragg panel. After its calibration the panel has been installed on its place in the optical block of the telescope and is ready for flight.

• Specifications:

  Parameter	ML	RAP	Si	LiF
  E-band (keV)	0.16-0.42	0.5-1.3	2-5	5-11
  lines	C, NeL, SiL	O, Ne, FeL	Si, S, Ar, Ca	Fe, Ni
  Resolving power	35-50	300-700	2000-5000	600-1200
  Reflectivity (%)	5-15	5-15	10-15	5-15

• Staff: At the AIP, we are 2 scientists engaged within the SODART project, Dr. Halm, Ingolf and Dr. Wiebicke, Hans-Joachim working on hardware calibration and software for simulation and in-flight calibration/observation.

• Software: Several software packages to prepare and support OXS observations are described in detail and can be down-loaded via ftp.

• Documentation: A detailed description of OXS and its properties can be found here.

• Papers: Our latest papers on this subject can be obtained as gziped ps-files from here.

• Comparison with high-resolution instruments on CHANDRA, XMM-NEWTON, and ASTRO-E missions is provided here.