HETGS Spectroscopy of the Cluster
Cooling Flow PKS 0745-191

The cluster of galaxies PKS 0745-191 is a bright, nearby (z=0.1028) cluster which is bright in X-rays and contains a strong cooling flow. Such cooling plasmas should be rich in X-ray line emission and make interesting targets for the HETGS. PKS 0745-191 is, however, an extended object making analysis of its spectrum more involved. The spectrum for the cluster emission was taken from fits to ASCA data for this object (Allen, Fabian, & Kneib 1996) [MNRAS, 279, 615].  Some relevant details of the model and simulations are given below.

Figure 1. - Simulated 100 ksec HETGS observation of PKS 0745-191. This image depicts part of the total ACIS-S array image which would be obtained. The 0th order image of the cluster is visible to the left of the image while the MEG and HEG dispersed spectra can be seen extending to the right. This simulation was created using MARX. Click on the image to see a larger version.

Figure 2. - This figure shows a plot of event dispersion distance versus the detected ACIS pulse height.  The 0th order photons comprise the bright vertical region clustered about D=0. The parabolas correspond to the higher order dispersed spectra. The additional information provided by ACIS's intrinsic spectral resolution will be useful in extracting the spectrum for a given grating and order.

Figure 3. - This figure is similar to Figure 2 in that it plots photon dispersion distance versus ACIS pulse height. In this case, we have used the known MEG grating period information to transform the MEG 1st order parabola above to a straight line. The bright vertical line corresponds to the MEG 1st spectrum of PKS 0745-191. Note that it is extended spatially. The curve to the left and right are the 0th spectrum and the HEG 1st order spectrum, respectively.

Figure 4. - An expanded view of the MEG 1st order spectrum isolated in Figure 2. This figure illustrates the spatial extent of the 1st order spectrum. Emission extends out to ~50 pixels or a radius of ~25 arcsec.

Figure 5. - The extacted MEG and HEG 1st order spectra for PKS 0745-191. An extraction region ~10 arcsec in radius was used so the emission visible is predominately due to the large cooling flow in PKS 0745-191.The top panel shows the input spectrum computed using SPEX.

Figure 6. - For comparison with Figure 5, the extracted ACIS pulse height spectrum is shown here. Since the dispersed spectra fall on all chips, the above spectrum reflects a mix of front and back side illuminated CCD spectral resolutions.

Simulation details:

Simulation courtesy of Michael Wise (MIT/ASC)

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Michael Wise - wise@space,mit.edu
Last Updated: July 22, 1997