Absolute effective areas of the HETGS

Abstract

Absolute e ective area measurements of the ight-con guration Chandra High-Energy Transmission Grating Spectrometer HETGS were performed at the X-ray Calibration Facility XRCF during Phase H testing. The results of these measurements are compared with e ective area predictions based on models of the individual HETGS components: the High Resolution Mirror Assembly HRMA, the High-Energy Transmission Grating HETG, and the AXAF CCD Imaging Spectrometer Spectroscopy array A CIS-S. The energy range from 0.48 to 8.7 keV was sampled at over 75 energies using x-rays produced by three of the sources available in the XRCF X-ray Source System XSS. The Double Crystal Monochromator DCM provided dense coverage of the range 0.9 keV to 8.7 keV; the High Resolution Erect Field grating Spectrometer HiREFS reference: speci cally HIREFS-SXR-1.75 grating monochromator from Hettrick Scienti c Inc. provided data points in the 0.48 keV to 0.8 keV range; and x-ray lines from several targets of the Electron Impact Point Source EIPS covered the range from 0.525 keV O-K to 1.74 keV Si-K. The absolute e ective area was measured as the ratio of the focal plane rate detected in a line to the line ux at the HRMA entrance aperture. A set of four Beam Normalization Detectors BNDs located around the HRMA were the prime source of ux determination. A variety of analysis techniques and considerations were applied including beam uniformity corrections, line deblending, and ACIS pileup. Uncertainties in the measurements are assigned based on counting statistics and estimates of analysis systematics; typically each measurement has an assigned error of order 10. The data indicate that we are very close to realizing our goal of a 10 absolute e ective area calibration for the rstorder e ective area. The measurement-model residuals are seldom outside a 20 range for both the High Energy Grating HEG and the Medium Energy Grating MEG rst-order areas. Systematic variation of the residuals appear at a level of -10 in the energy range below 1.3 keV; in the 2.5 keV to 5 keV range a consistent +3 to +7 over prediction is seen. The regions of greater systematic variation, 1.3 to 2.5 keV and above 5 k eV, are most likely dominated by uncompensated DCM beam uniformity e ects and ACIS grade migration e ects respectively.

TheChandraHigh‐Energy Transmission Grating: Design, Fabrication, Ground Calibration, and 5 Years in Flight

“…The ACIS detector was defocused by 5 to 40 mm to reduce pileup caused when more than one photon arrives in a small region of the detector during a single integration (Davis 2001b(Davis , 2003 by spreading the detected events over a larger detector area, as seen in Figure 19. A variety of analysis techniques and considerations were applied to analyze these data (Schulz et al 1998). Chief among them for the monochromator data sets were beam uniformity corrections to the effective flux based on extensive measurements and modeling carried out by the MSFC project science group (Swartz et al 1998).…”

The Chandra X-Ray Observatory (CXO)

“…In addition to the Calibration Reports, some of the results appear in these 11,12,13,14,15,16,17,18,19,20,5 and previous 21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,9,10 proceedings.…”

In-flight calibration of the Chandra high-energy transmission grating spectrometer

“…These disperse X-rays to the focal plane detector, which is usually the Advanced CCD Imaging Spectrometer (ACIS). 5 Ground-based calibration observations have been previously reported [6][7][8][9][10][11] and are summarized in the HETGS Ground Calibration Report † These reports provide detailed ground-based measurements and modeling of various aspects of the HETGS such as the line response function (LRF) and the grating efficiencies. Here, we report on analysis of many observations obtained with the HETGS during in-flight calibration and instrument checkout.…”