Note: This page describes the RMFs for use with PHA-based PI. As of CALDB 4.2/CIAO 4.2 (December 2009), the default is to calculate PI from scaled SUMAMPS (SAMP) rather than PHA. New RMFs have been created for use SAMP-based PI, see this page.
We have developed RMFs for the HRC-I and HRC-S. This page discusses the creation of and justification for the RMF and provides grids in hardness-ratio and quantile-width spaces for some common spectral models, as calculated with the new RMF.
Vinay Kashyap & Jennifer Posson-Brown
November 2005
The intrinsic energy resolution of the HRC is poor compared with the ACIS, but it does have some ability to discriminate between hard and soft spectra. Lab tests of HRC-I pulse-height distributions obtained during sub-assembly calibration show a monotonic trend in the median PHA for line energies below 2 keV (see Figure 7.7 of the Chandra Proposers' Observatory Guide).
This spectral discrimination is also seen in flight data. We have analyzed data from the flaring variable coronal source AR Lac, which has been regularly observed since 1999 as a calibration source to monitor the HRC-I gain and QE, and in the adjacent plot we show the count-rate and the corresponding median PI computed for each observation (each approximately 2 ks in duration) with off-axis values < 8 arcmin. When a coronal source flares, the plasma temperature is usually higher, and consequently the spectrum is harder; a (weak) correlation is therefore to be expected between count-rate and spectral hardness, and is indeed detected in the data. A correlation of 0.27 is observed, with an error of 0.02 determined after a Monte Carlo simulation of the individual errors. Pearson's coefficient rho is 0.24, with a p-value of 0.02, and Kendall's Rank correlation coefficient tau is 0.17, with a p-value of 0.01.
Using observations of HR1099 carried out using the HRC-I/LETG at various locations on the detector (ObsIDs 1388, 1389, 1392, 1393), we have constructed a response matrix for the HRC-I (see Kashyap & Posson-Brown 2005). The following plot from Kashyap & Posson-Brown 2005 summarizes our analysis.
Results of fitting wavelength "slices" of co-added HRC-I/LETG HR 1099 observations with Gaussians. The best-fits means are shown by diamond points, with one sigma error bars. The shaded region shows the best-fit Gaussian sigmas. The dashed lines show linear fits to the means. We constructed the RMF from these linear fits.
The HRC-I RMF can be used to calibrate hardness ratios or quantile color-color diagrams (QCCD) to distinguish between gross differences in the spectra. We recommend the QCCD, as it is relatively less dependent on temporal variations in the gain that are known to exist, and are not yet accounted for, in the gain-correction maps.
Here we provide grids in hardness-ratio and quantile-width spaces for some common spectral models, as calculated using the HRC-I RMF derived above and a nominal on-axis ARF (v2.2). The grids were calculated using Sherpa. For the hardness ratio, we choose three bands in PI,
The color-color grid for a powerlaw model, calculated for various values of the powerlaw index Gamma (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The color-color grid for a MEKAL model, calculated for relatively low values of the plasma temperature kT [keV] (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The color-color grid for a MEKAL model, calculated for relatively high values of the plasma temperature kT [keV] (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The color-color grid for a Blackbody model, calculated for various values of the temperature kT [keV] (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The quantile-width grid for a powerlaw model, calculated for various values of the powerlaw index Gamma (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (red loci).
The quantile-width grid for a MEKAL model, calculated for relatively low values of the plasma temperature kT [keV] (blue loci) and absorption column N_{H} [10^{22} cm^{-2}] (red loci).
The quantile-width grid for a MEKAL model, calculated for relatively high values of the plasma temperature kT [keV] (blue loci) and absorption column N_{H} [10^{22} cm^{-2}] (red loci).
The quantile-width grid for a Blackbody model, calculated for various values of the temperature kT [keV] (yellow loci) and absorption column N_{H} [10^{22} cm^{-2}] (red loci).
Vinay Kashyap & Jennifer Posson-Brown
November 2006
Results of fitting Gaussians to wavelength "slices" of co-added HRC-S/LETG observations of RXJ1856, PKS 2155-304, Capella, V4743Sgr, and Mkn 421. The best-fits means are shown by diamond points, with one sigma error bars. The shaded region shows the best-fit Gaussian sigmas. The dashed line shows a linear fits to the means. We constructed the RMF from this linear fit.
Here we provide grids in hardness-ratio and quantile-width spaces for some common spectral models, as calculated using the HRC-S RMF derived above and a nominal on-axis ARF (v2.2). The grids were calculated using Sherpa. For the hardness ratio, we choose three bands in PI,
The color-color grid for a powerlaw model, calculated for various values of the powerlaw index Gamma (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The color-color grid for a MEKAL model, calculated for relatively low values of the plasma temperature kT [keV] (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The color-color grid for a MEKAL model, calculated for relatively high values of the plasma temperature kT [keV] (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The color-color grid for a Blackbody model, calculated for various values of the temperature kT [keV] (green loci) and absorption column N_{H} [10^{22} cm^{-2}] (yellow loci).
The quantile-width grid for a powerlaw model, calculated for various values of the powerlaw index Gamma (red loci) and absorption column N_{H} [10^{22} cm^{-2}] (blue loci).
The quantile-width grid for a MEKAL model, calculated for a variety of plasma temperature kT [keV] (red loci) and absorption column N_{H} [10^{22} cm^{-2}] (blue loci).
The quantile-width grid for a Blackbody model, calculated for various values of the temperature kT [keV] (red loci) and absorption column N_{H} [10^{22} cm^{-2}] (blue loci).
We thank Hong Jae Sub, Doug Burke, and Andreas Zezas for assistance with generating the grids, Peter Freeman for useful discussions on the structure of RMFs, and Brad Wargelin for help with generating the HRC-S RMF.
Last modified: 09/25/12
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