ART-XC: Astronomical Roentgen Telescope – X-ray Concentrator

ART Logo

ART-XC on SRG

ART-XC, the Astronomical Roentgen Telescope - X-ray Concentrator, is one of two instruments aboard the Spectrum-Roentgen-Gamma (SRG) high-energy astrophysics observatory. SRG is a joint Russian-German mission launched from the Baikonur, Kazakhstan, Cosmodrome 13 July 2019 into a halo orbit about the Sun-Earth L2 Lagrange point about 1.5 million kilometers from Earth in the direction opposite to the Sun.

SRG orbit

SRG began a 4-year all-sky survey on 13 Dec 2019. At the conclusion of the all-sky survey phase, SRG is planned to carry out over two years of pointed observations of targets of interest.

The ART-XC payload is a focussing X-ray instrument consisting of seven nearly identical and co-aligned telescopes each comprised of a mirror module assembly focussing X-ray photons onto a double-sided strip CdTe detector capable of registering the position, energy, and arrival time of events over a 36x36 arcminute field-of-view. ART-XC telescopes operate most efficiently in the 4 to 12 keV X-ray band though theu are sensitive up to 30 keV for bright sources.

ART instrument schematic

This schematic of the ART-XC instrument shows the array of 7 co-aligned mirror modules, sunshield, and star tracking camera at one end of the carbon-fiber optical bench and the matching array of 7 detectors, collimators and passive thermal control at the other end of the optical bench. The focal length is 2.7 meters.

Mirror Modules

ART mirror schematic

NASA's Marshall Space Flight Center designed, fabricated and calibrated the ART-XC X-ray mirror module assemblies. Each module consists of 28 nested, co-aligned, Wolter-I type double-reflection grazing incidence mirror shells. The shells are made of a Ni-Co alloy in an electroformed replication process. The total effective area of the 7-telescope system is 385 sq. cm at 8 keV. The on-axis half-power diameter is about 30 arcsecond. This cut-away view of an ART-XC mirror module showing the nested mirror shells (gray), the mounting `spider' located at the X-ray entrance end of the module and related hardware. Each mirror module is approximately 600~mm long and 175~mm diameter.

Focal Plane Detectors

The Russian Space Research Institute developed the focal plane X-ray detectors. They are built from CdTe crystals with both top and bottom electrodes in a double-sided strip configuration forming a 48x48 pixel array. The pixel size is 45x45 arcsec.

ART detector photo

This photo of an ART-XC focal plane detector hybrid integrated circuit shows the CdTe crystal (gold square) held to a 3-layer ceramic mounting structure (white). The two readout ASICs are visible on adjacent edges of the crystal. External connections to the board provided through flexible circuit boards that extend outside the bottom ceramic mounting disk are also visible.