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) Type CCD CHIPX$^a$   Wavelength (Å) Type CCD CHIPX$^a$
6.360$\pm$0.010 node boundary 9 171-172   21.810$\pm$0.020 cool pixel 4 252-254
6.980$\pm$0.005   9 90   22.720$\pm$0.010 node boundary 4 171-172
7.030$\pm$0.005   9 83   22.770$\pm$0.005 cool pixel 4 167
7.630$\pm$0.005   9 6   22.950$\pm$0.005 cool pixel 4 152
7.666$\pm$0.035 chip gap       23.380$\pm$0.010 cool pixel 4 113-114
9.090$\pm$0.010 node boundary 8 171-172   24.115$\pm$0.005 cool pixel 4 51
9.650$\pm$0.005 cool pixel 8 104   24.702$\pm$0.055 chip gap    
10.140$\pm$0.015 cool pixel 8 44-46   25.870$\pm$0.020 cool pixel 3 249-252
14.440$\pm$0.005 cool pixel 6 267   26.640$\pm$0.005 cool pixel 3 186
15.230$\pm$0.025 cool pixel 6 183-187   26.820$\pm$0.010 node boundary 3 171-172
15.310$\pm$0.005 cool pixel 6 177   27.340$\pm$0.005 cool pixel 3 129
15.360$\pm$0.010 node boundary 6 171-172   27.740$\pm$0.005 cool pixel 3 96
15.830$\pm$0.005 cool pixel 6 124   28.260$\pm$0.005 cool pixel 3 54
17.072$\pm$0.040 chip gap       28.780$\pm$0.005 cool pixel 3 12
17.550$\pm$0.005 cool pixel 5 301   28.942$\pm$0.055 chip gap    
18.360$\pm$0.025 cool pixel 5 222-226   30.350$\pm$0.005 cool pixel 2 237
18.670$\pm$0.005 cool pixel 5 194   31.195$\pm$0.010 node boundary 2 171-172
18.910$\pm$0.010 node boundary 5 171-172   31.270$\pm$0.020 cool pixel 2 164-167
18.960$\pm$0.005 cool pixel 5 168   33.446$\pm$0.050 chip gap    
19.490$\pm$0.015 cool pixel 5 115-117   34.010$\pm$0.020 bad/cool pixel 1 304-307
19.670$\pm$0.005 cool pixel 5 100   35.825$\pm$0.010 node boundary 1 171-172
19.900$\pm$0.005 cool pixel 5 79   36.175$\pm$0.005 cool pixel 1 146
20.753$\pm$0.045 chip gap       36.760$\pm$0.005 cool pixel 1 103
$^a$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) Type CCD CHIPX$^a$   Wavelength (Å) Type CCD CHIPX$^a$
6.180$\pm$0.005   9 103   24.920$\pm$0.020 cool pixel 3 265
6.380$\pm$0.020   9 93-96   25.790$\pm$0.005 cool pixel 3 192
6.540$\pm$0.005   9 80   26.130$\pm$0.005 cool pixel 3 164
6.840$\pm$0.005   9 41   28.223$\pm$0.050 chip gap    
7.050$\pm$0.005   9 13   28.590$\pm$0.005 cool pixel 2 316
7.241$\pm$0.040 chip gap       30.730$\pm$0.005 cool pixel 2 142
7.960$\pm$0.015 cool pixel 8 245-246   31.310$\pm$0.005 cool pixel 2 97
8.605$\pm$0.005 cool pixel 8 167   32.676$\pm$0.050 chip gap    
9.105$\pm$0.005 cool pixel 8 103   33.330$\pm$0.005 cool pixel 1 291
9.365$\pm$0.015 cool pixel 8 71   33.590$\pm$0.005 cool pixel 1 272
9.920$\pm$0.015 cool pixel 8 6   33.850$\pm$0.005 cool pixel 1 252
10.056$\pm$0.040 chip gap       34.270$\pm$0.005 cool pixel 1 221
13.152$\pm$0.050 chip gap       34.460$\pm$0.005 cool pixel 1 207
14.690$\pm$0.010 cool pixel 6 174-175   35.110$\pm$0.005 cool pixel 1 159
14.940$\pm$0.020 cool pixel 6 148-151   35.160$\pm$0.005 cool pixel 1 156
16.504$\pm$0.055 chip gap       35.780$\pm$0.005 cool pixel 1 110
16.580$\pm$0.005 cool pixel 5 332   36.850$\pm$0.005 cool pixel 1 33
18.700$\pm$0.005 cool pixel 5 126   37.140$\pm$0.005 cool pixel 1 12
$^a$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
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