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.

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.