Toward the calibration of the HETGS line response function

The high-energy transmission grating for AXAF was tested with the AXAF HRMA during December 1996 through April 1997 at NASA's MSFC X-Ray Calibration Facility. This first-use of the complete HETG spectrometer (HETGS) produced some low-level surprises in the line response function (LRF) and indicate that the HETG is meeting or exceeding its resolving-power specifications. This paper reviews the ingredients of the HETGS LRF, describes the pre-XRCF HETG sub-assembly measurements, presents an overview of the XRCF LRF-related measurements and data, and summarizes our knowledge of the HETG contribution to the HETGS line response function. Two low-level effects, grating scatter and grating misalignment, were uncovered in this testing.