XMM-Newton Science Analysis System: Users' Guide

5.7.1 Generating RGS images

Once the axes have been selected and any selection criteria specified, pushing the Image button initiates dialogue panels that includes an Image section like that shown in Fig. 30 which gives the opportunity to review the choices made. The BETA_CORR/PI images, commonly known as banana plots, are improved by overruling the default y-range by checking the withyranges box and setting

yimagemin
yimagemax

Fig. 31 shows plots of the merged RGS1 events. These plots are orthogonal projections of the all-important BETA_CORR,XDSP_CORR,PI 3-D RGS data space of the merged list of all the events detected in the observation, thus showing all the features, both good and not so good, of RGS data. The edges are clear of the 9 CCDs, numbered 1-9 from right to left. In both plots, wavelength and dispersion angle increase from left to right.

Figure 31: The BETA_CORR/XDSP_CORR and BETA_CORR/PI plots produced by xmmselect using ds9 for the merged RGS1 and RGS2 event lists of Mkn421 before filtering, thus showing all hot pixels and columns and other blemishes in addition to the bright smooth continuum of this active galaxy. It can take some experience with ds9 Zoom, Color and Scale controls to display the data to best effect. These images used sls colours on a logarithmic scale.

From quite early in the mission, each RGS has been missing data from one CCD because of electronics failures, RGS1 CCD7 and RGS2 CCD4, that happily do not cover the same wavelengths. The pointing coordinates were evidently chosen well enough to put this bright source central in the aperture. The source was bright enough to be seen up to 4th or even a weak 5th order in the characteristic hyperbolic-shaped areas occupied by photons that have passed through the gratings. There are plenty of hot pixels and columns and the so-called fixed pattern noise shows as the herring-bone pattern in CCDs 8 and 9. Calibration sources of F K$\alpha$ at PI$=677$eV span CCDs 2&3 and 7&8 ; and Al K$\alpha$ at PI$=1487$eV span CCDs 3&4 and 8&9.

The locations of the selection regions may be checked using the task rgsimplot

http://xmm.esac.esa.int/sas/current/doc/rgsimplot/index.html

which plots them over BETA-XDSP and BETA-PI images that are, in this case, most usefully generated from the screened events files. Fig. 32 shows such an example.

Figure 32: The BETA_CORR-XDSP_CORR and BETA_CORR-PI images produced by xmmselect from the screened event list can be shown with the selection regions using rgsimplot.