Last modified: 24 September 2021

URL: https://cxc.cfa.harvard.edu/ciao/why/hrc_qe.html

HRC-S QE/QEU


HRC-S QE vN0016 & QEU vN0015

New set of HRC-S mean quantum efficiency (QE) and QE uniformity (QEU) files was released for HRC-S in CALDB 4.9.6 (21 September 2021), upgrading the prior set of QE and QEU files introduced in CALDB 4.9.2.1 and 4.9.4, repsectively.

For the QE, an additional epoch was added to account for the HRC-S high-voltage change on 2021 May 14, which has a mean QE value that is 1.106 times higher than the prior epoch, beginning on 2012 March 29. This change was needed for HRC-S/LETG fluxes observed from HZ 43 after the voltage change to match those expected from the zeroth and dispersed orders.

For the QEU, an additional file has been added, coinciding with the 2021 high-voltage change. The update changes the detector's outer plates' wavelenght-dependent corrections to match expected HZ 43 flux while accounting for the detector degradation over time.

Finally, the linear ramps introduced in QE N0014 for wavelengths shorter than 20Å, versus time, have been moved to the QEU N0015. This results in the removal of the annually-varying QE N0014 files, as all the secular variations are being included with the QEU correction files.

HRC-S QE vN0013 & vN0014

A new mean quantum efficiency (QE) file was released for HRC-S in CALDB 4.6.9 (23 September 2015), modifying the existing QE from CALDB 4.6.5 (14 December 2014).

The N0014 HRC-S QE is the result of modifications to the HRC-S/LETG gRMFs, however, since the overall gRMF × gARF response did not change, an overall adjustment to the QE, which affects the grating ARF shape was needed.

The N0013 HRC-S QE is from analyses of HRC-S/LETG observations of the hot white dwarf HZ43 have indicated a loss in gain at certain plate locations in both positive and negative spectral orders. At higher energies, analyses of interleaved series of blazar data with the LETG in combination with both ACIS-S and HRC-S detectors indicate that derived fluxes for the latter are systematically lower than the former. A downward revision of the HRC-S quantum efficiency (QE) for photon energies above that of the carbon K edge is the current best-guess of the correction required to reconcile derived fluxes.

The new file will be used by default when creating exposure maps or grating ARFs in CIAO.

HRC-S QEU vN0012

The HRC-S QEU file was upgraded to version N0012 in CALDB 4.8.4 (03 September 2019). Version N0012 of the HRC-S QEU takes into account the accelerated QE degradation with time.

This QEU fixes the time-dependence in the HRC-S for all observational periods from 1999 through the present. Since the changes are normalized to be zero at 2008, the gARFs and exposure maps will not change for observations with DATE-OBS between 2008-01-01T00:00:00 and 2009-01-01T00:00:00. Since the high voltage change in 2012 April, the wavelength- independent QE decline has been updated from 2.51 to 2.55%/yr for zeroth order, and from 2.35 to 2.38%/yr for dispersed orders.

The most recent QE and QEU calibration will automatically be chosen from the CALDB when creating exposure maps, imaging ARFs, or grating ARFs for HRC-S data.