About Chandra Archive Proposer Instruments & Calibration Newsletters Data Analysis HelpDesk Calibration Database NASA Archives & Centers Chandra Science Links


HRC-I Quantum Efficiencey Verification

using White Dwarf HZ 43

K. Tabetha Hole, Deron Pease, Hank Donnelly

For this study we employed the hot white dwarf HZ 43 (ObsID 1514) to perform HRC-I on-axis QE calibration/confirmation over the low energy range 0.065 - 0.20 keV.

Predicted Counts

Martin Barstow (MB - Leicester University, UK) and David Finley (DF - Eureka Scientific) each provided source models for HZ 43 (see models below). Using IDL to convolve the source models with the current state of the HRC-I QE model (version 1.1), we were to generate predicted HRC-I counts.

The predicted counts with total model uncertainties are:

14060   ±   15.0%       - MB
11610   ±   15.0%       - DF

Observed Counts

The HRC-I observation of HZ 43 was conducted with the LETG inserted. To compare with the no-grating HRC-I on-axis QE, we extracted the observed counts from a circle around 0th order, and accounted for attenuation by the LETG. A very large HRC-I background region was defined as the active detector minus the source region.

The background-subtracted observed counts are:    7752   ±   1.2%

Comparison with Error Analysis

The source models for HZ43 have uncertainties of ~15.0%. The HRC-I QE over this range was not calibrated prior to flight. An educated guess at the low energy HRC-I QE was made, with the uncertainty stated to include all physically possible values. Thus, we rely on the HZ 43 source models to constrain the HRC-I QE and provide the total model uncertainty of at least ~15%.

With the MB model the HRC-I sees 81.4% less (absolute difference) than predicted by the model. With the DF model the HRC-I sees 49.8% less than predicted by the model. Clearly, over this low energy regime the HRC-I QE model is currently too high, and must be modified (lowered) to match the predicted and observed within allowed uncertainties.

Source Models

MBmod Source Model      DFmod Source Model      Source Models Plotted (.ps)

Contact CXC Calibration (cxccal@cfa.harvard.edu) for further information

Last modified: 09/25/12

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory.
60 Garden Street, Cambridge, MA 02138 USA.    Email: cxcweb@head.cfa.harvard.edu
Smithsonian Institution, Copyright © 1998-2004. All rights reserved.