Any measurement made by Chandra involves the total throughput of the telescope; in that sense this study is the verification of the on-axis Effective Area (EA). However, by making the reasonable assumption that the errors in the HRMA on-axis effective area and the transmission of the HRC UV/Ion Shield are much less significant than the errors on the HRC MCP QEs, this study becomes a Quantum Efficiency (QE) verification.

HRC on-axis QE verification is achieved by either 1) cross-calibration with ACIS observations to develop source flux models, or 2) comparison of HRC data to experimental source flux models from the literature. The tables below summarize our findings; details on models and procedure may be obtained by following the links under the Source column.
 

Column Definitions

• Source:    source name; follow this link for analysis details
• Energy Band:    energy regime in keV for which the source is usefull for this calibration
• Predicted Cts:    model-predicted counts (HRC-I,-S flight QE models version 1 can be found here); for HZ 43 two source models are compared
• Observed Cts:    Chandra HRC observed counts with statistical % errors
• % Diff:    (observed counts - predicted counts) / observed counts
• Allowed % Diff:    Total allowed % uncertainties by model (source model + instrument response model)

• HRC-I (Kenter, et al.)    
• HRC-S (Kraft, et al.)

Caveats

• Source Models: For this on-orbit calibration, we have attempted to employ the most current and highest fidelity source models to ensure a robust QE verification. However, if you know of better models than those used here for these sources, we encourage you to share that information with us.
• Source Variability: The above sources were chosen because they show little to no variability over time. Also, to minimize any potential source variability during cross-calibration efforts, the HRC and ACIS observations were conducted as closely as possible in time. Any unrealized source variability would of course lead to more uncertainty.

Last modified: 09/25/12

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