XMM-Newton Users Handbook


3.4.5.2 RGS Multipointing Mode (MPM)

Most RGS observations are performed with the target at a central fixed location on the RGS detectors, close to the telescope axes. There are, however, some circumstances in which observers might consider the alternative “RGS Multipointing Mode” (MPM).

A small proportion of defects comprising bad or “cool” columns or pixels are inevitable in CCD detectors. In a dispersive instrument like the RGS, these detector defects, usually one pixel wide, correspond to fixed narrow wavelength intervals of about 10 mÅ (see Tables 13 and 14). These wavelength defects sometimes coincide with features in the source spectrum that are important for the scientific success of an observation. When these circumstances arise, it is possible to change the spacecraft pointing in order to move the defects away so that more important parts of the spectrum are not affected. Also the small gaps between the CCDs may be filled with data in a similar way using this method.

The RGS Multipointing mode uses five different pointings, with offsets in the dispersion direction of 0, $\pm$15 and $\pm$30 arcsec, corresponding to 0, $\pm$35 and $\pm$69 mÅ. In this way, the maximum flux loss in a spectral line is reduced significantly, and it becomes easier to distinguish weak absorption lines from defects.

The user is referred to § 4.6.2 for full details and a discussion of the implications of the use of this mode in the performance of EPIC-pn.


Table 13: RGS1 detector defects and corresponding wavelengths for on-axis sources.
Wavelength (Å) CCD CHIPX$^a$ Type   Wavelength (Å) CCD CHIPX$^a$ Type
6.37 9 171 node gap 22.19 4 220 cool pixel  
7.70 8/9   chip gap 22.75 4 171-172 node gap  
8.93 8 193 cool pixel 22.80 4 167 cool pixel  
9.11 8 171-172 node gap 22.97 4 152-153 hot/cool pixels  
9.66 8 104 cool pixel 23.40 4 113-115 hot/cool pixels  
10.15 8 44-45 cool pixels 24.12 4 51 cool pixel  
14.45 6 266-267 hot/cool pixels 24.29 4 35-36 cool pixels  
15.25 6 183-187 hot/cool pixels 24.76 4/3   chip gap  
15.33 6 177 cool pixel 25.88 3 250 cool pixel  
15.39 6 171-172 node gap 26.66 3 186 cool pixel  
15.45 6 165 cool pixel 26.85 3 171-172 node gap  
15.50 6 160 cool pixel 27.35 3 129-130 cool pixels  
15.84 6 124-125 cool pixels 27.65 3 105 cool pixel  
16.21 6 88 hot pixel 27.76 3 96 cool pixel  
16.43 6 65 cool pixel 28.27 3 54 cool pixel  
17.12 6/5   chip gap 28.78 3 12 cool pixel  
17.56 5 301 cool pixel 29.01 3/2   chip gap  
18.36 5 224-225 cool pixels 30.37 2 237 cool pixel  
18.69 5 194 cool pixel 31.22 2 171-172 node gap  
18.93 5 171-172 node gap 31.29 2 165-166 cool pixels  
18.96 5 168 cool pixel 33.51 2/1   chip gap  
19.51 5 115-116 cool pixels 34.02 1 304-307 hot/cool pixels  
19.68 5 100 cool pixel 35.85 1 171-172 node gap  
19.90 5 79 cool pixel 36.77 1 104 cool pixel  
20.81 5/4   chip gap 36.78 1 103 cool pixel  
21.82 4 252-253 cool pixels 37.35 1 62 cool pixel  
$^a$Pixel position of defect in detector x-coordinates. The conversion to wavelength is given only for on-axis sources.

Figure 88: Scheme of the position of the RGS detector defects in wavelength space.
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\epsfig{file=figs/rgs_badpix.ps,height=\linewid...
...ngle=90,bbllx=290,bblly=54,bburx=558,bbury=738}
\end{center}
\end{figure}


Table 14: RGS2 detector defects and corresponding wavelengths for on-axis sources. Since the introduction of single-node operations, the node boundary that applies between the two nodes of the RGS1 CCDs is no longer relevant in RGS2.
Wavelength (Å) CCD CHIPX$^a$ Type   Wavelength (Å) CCD CHIPX$^a$ Type
6.17 9 130 cool pixel   24.92 3 265-266 hot/cool pixels
6.37 9 103 cool pixel   25.81 3 192 hot pixel
6.43 9 94 hot pixel   26.15 3 164 cool pixel
7.18 9/8   chip gap   28.20 3/2   chip gap
7.59 8 292 cool pixel   28.53 2 316 cool pixel
7.96 8 246 cool pixel   30.75 2 142 cool pixel
8.60 8 167 cool pixel   31.33 2 97 cool pixel
9.12 8 103 cool pixel   32.65 2/1   chip gap
9.38 8 71 cool pixel   33.34 1 291 cool pixel
9.57 8 48 cool pixel   33.60 1 272 hot pixel
9.91 8 6 cool pixel   33.87 1 252 cool pixel
10.01 8/7   chip gap   34.29 1 221 cool pixel
13.10 7/6   chip gap   34.48 1 207 hot pixel
14.71 6 174-175 cool pixels   35.13 1 159 hot pixel
14.95 6 149-150 cool pixels   35.17 1 156 cool pixel
16.47 6/5   chip gap   35.79 1 110 cool pixel
16.58 5 332 cool pixel   36.84 1 33 hot pixel
18.72 5 126 cool pixel   37.12 1 12 cool pixel
$^a$Pixel position of defect in detector x-coordinates. The conversion to wavelength is given only for on-axis sources.

European Space Agency - XMM-Newton Science Operations Centre