Calibration of the ART-XC mirror modules at MSFC

Abstract

The Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Roentgen Gamma (SRG) spacecraft in 2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Theta. We used a King function to approximate the radial profile of the near on-axis PSF (Theta<9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9<Theta<24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module.Comment: 16 pages, 10 figures, 5 tables, Accepted in Experimental Astronom

SRG/ART-XC all-sky X-ray survey: Catalog of sources detected during the first year

“…We adopted the vignetting function from the results of extensive ray-tracing simulations of the ART-XC X-ray mirrors (Pavlinsky et al 2021). The P (x 0 |x) function was precomputed for a fine grid of positions in the ART-XC FoV using the ART-XC PSF model obtained from the results of ground calibrations of the mirror systems (Gubarev et al 2014;Krivonos et al 2017;Pavlinsky et al 2018Pavlinsky et al , 2019aPavlinsky et al ,b, 2021. Interpolation was then used to evaluate P (x 0 |x) for a photon at a given position in the ART-XC FoV.…”

The ART-XC telescope on board the SRG observatory

“…The MSFC fabricated, tested, and calibrated eight identical X-ray MSs for ART-XC (see Fig. 2) (Gubarev et al 2012, Gubarev et al 2014, Krivonos et al 2017; seven of them were installed in the flight model of the telescope and the eighth became a spare.…”

“…First, the ART-XC flight MSs were calibrated at the NASA/MSFC Stray Light Test Facility (Gubarev et al 2014;Krivonos et al 2017). For each mirror system, the half-power diameter (HPD), the point-spread function (PSF) with high resolution, and the effective area at various off-axis angles and azimuths were measured.…”

“…13. Table 3 (Krivonos et al 2017). The PSF was obtained by averaging measurements at four azimuth angles.…”

“…In Fig. 25, the PSF radial profile measured in scanning mode observations of a bright X-ray source (GX 3+1) near the Galactic centre is compared to the radial profile of the PSF measured during the calibrations of the MSs at the MSFC Stray Light Test Facility (Krivonos et al 2017). To this end, the PSF measured at MSFC was convolved with a sliding box of the detector pixel size (45 ) and then averaged over the field of view taking in account the vignetting function inferred from ray-tracing simulations.…”