  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.
