National Aeronautics and Space Administration

Spectr-Roentgen-Gamma (SRG)

The Spectr-Roentgen-Gamma (SRG) is a Russian-German high energy astrophysics mission launched on July 13, 2019 from the Baikonur Cosmodrome. After travelling to the Earth-Sun L2 Lagrange point, the instruments began the first of eight planned sky surveys in December 2019. Mission plans call for four years of operations in scanning mode, building all-sky maps over the course of six months. Once completed, the observatory with shift to pointed observations at specific targets of interest. The original mission calls for seven years of operations.

The mission occasionally appears as “Spectrum X-Gamma” (SXG) in English. X-rays are often refered to as Röntgen or Roentgen rays in other countries (and in the case of this mission specifically, in Russia and Germany) named after their discoverer Wilhelm Conrad Röntgen.

Despite the “Gamma” appelation in the mission name, the satellite carries no gamma-ray instrument. The reference was retained for historical reasons, as the mission’s earlier proposals called for additional gamma-ray detectors.

Mission Characteristics

Lifetime

Energy Range

Special Features

Payload

• The Extended Roentgen Survey with an Imaging Telescope Array (eROSITA) instrument consists of seven telescopes with 54 nested mirror segments to focus X-rays onto a CCD detector (0.2-10 keV) with an on-axis 18 arcsec HEW. The Filed of view is 0.81 sq deg and the energy resolution is 138 eV at 6 keV. The instrument and mirrors were built by the Max Planck Institute of Extraterrestrial Physics, using a CCD design based on the successful XMM-Newton CCD detectors. They are active cooled to -90° C for improved sensitivity.
• The Astronomical Roentgen Telescope - X-ray Concentrator (ART-XC) is also an array of seven telescopes in a nested shell design, though with fewer mirror segments (28 per telescope) and a 45 arcsecond resolution in a 36 arcminute field of view spanning 5–30 keV. The detector unit in each telescope is a CdTe crystal with double-side strip detectors with an effective area of 400 cm² and 1.2 keV @ 14 keV spectral resolution and a timing resolution of about 1 ms. The instrument was build at the Russian State Nuclear Center and the iridium-coated mirror system was developed and calibrated at NASA’s Marshall Space Flight Center.

Science Highlights

• First all-sky imaging in the X-ray hard band

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