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)	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.