XMM-Newton Users Handbook


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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   22.75 4 171-172 node gap
7.70 8/9   chip gap   22.80 4 167 cool pixel
8.93 8 193 cool pixel   22.97 4 152-153 hot/cool pixels
9.11 8 171-172 node gap   23.40 4 113-115 hot/cool pixels
9.66 8 104 cool pixel   24.12 4 51 cool pixel
10.15 8 44-45 cool pixels   24.29 4 35-36 cool pixels
14.45 6 266-267 hot/cool pixels   24.76 4/3   chip gap
15.25 6 183-187 hot/cool pixels   25.88 3 250 cool pixel
15.33 6 177 cool pixel   26.66 3 186 cool pixel
15.39 6 171-172 node gap   26.85 3 171-172 node gap
15.45 6 165 cool pixel   27.35 3 129-130 cool pixels
15.50 6 160 cool pixel   27.65 3 105 cool pixel
15.84 6 124-125 cool pixels   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 cool pixels
19.68 5 100 cool pixel   35.85 1 171-172 node gap
19.90 5 79 cool pixel   36.20 1 146 hot pixel
20.81 5/4   chip gap   36.77 1 104 cool pixel
21.82 4 252-253 cool pixels   36.78 1 103 cool pixel
22.19 4 220 cool pixel   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.


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 cool pixels
6.37 9 103 cool pixel   25.81 3 192 cool pixel
7.18 9/8   chip gap   26.15 3 164 cool pixel
7.59 8 292 cool pixel   28.20 3/2   chip gap
7.96 8 246 cool pixel   28.53 2 316 cool pixel
8.60 8 167 cool pixel   30.75 2 142 cool pixel
9.12 8 103 cool pixel   31.33 2 97 cool pixel
9.38 8 71 cool pixel   32.65 2/1   chip gap
9.57 8 48 cool pixel   33.15 1 305 hot pixel
9.91 8 6 cool pixel   33.34 1 291 cool pixel
10.01 8/7   chip gap   33.60 1 272 cool pixel
13.10 7/6   chip gap   33.87 1 252 cool pixel
13.82 6 267 hot pixel   34.29 1 221 cool pixel
14.59 6 187 hot pixel   34.48 1 207 cool pixel
14.71 6 174-175 cool pixels   35.13 1 159 cool 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 cool 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.


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Next: 3.4.6 RGS specific proposal submission information Up: 3.4.5 Operating Modes of the RGS Previous: 3.4.5.1 RGS Small Window Mode
European Space Agency - XMM-Newton Science Operations Centre