On-Board Instruments

The INTEGRAL payload consists of two main gamma-ray instruments: the Spectrometer, SPI, and the Imager, IBIS. Each of them has both spectral and angular resolution, but they are differently optimized in order to complement each other and to achieve overall excellent performance. These instruments are supported by two monitor instruments which provide complementary observations in the X-ray and optical energy bands: the X-Ray Monitor, JEM-X, and the Optical Monitoring Camera, OMC. The Spectrometer, Imager and JEM-X share a common principle of operation: they are all coded-mask telescopes. More details are given in Tables 1 and 2. The continuum sensitivities of the INTEGRAL instruments are shown in Figure 4. The detailed description of each instrument is given in the corresponding User Manuals [1], [2],[3],[4].

The coordinate system incident to the INTEGRAL is an X, Y, Z orthogonal coordinate system with the origin at the center of the separation plane between spacecraft and launch adaptor, see Figure 3. The X-axis is perpendicular to this spacecraft/launcher separation plane, pointing positively from the separation plane towards the spacecraft (i.e. the X-axis is the pointing direction). The Z-axis is orthogonal to the solar array surface, pointing positively to the sun, i.e. the sun is illuminating the payload module on the IBIS side, while leaving SPI in the shadow. The Y -axis completes the coordinate system.

Table 1: Key performance parameters of SPI & IBIS Instruments.

	SPI	IBIS
Energy range	20 keV Ð 8 MeV	15 keV Ð 10 MeV
Detector	19 Ge detectors cooled to 85 K	16384 CdTe detectors (ISGRI),
		4096 CsI detectors (PICsIT)
Detector area (cm2 )	500	2600 (CdTe), 3100 (CsI)
Spectral resolution (FWHM)	2.3 keV @ 1.3 MeV	9 keV @ 100 keV
Field of view (fully coded)	16 (corner to corner)	9
Angular resolution (FWHM)	2.5 (point source)	12
Source location (radius)	1.3 (depending on the source strength)	1 (for 10 source)
Absolute timing accuracy (3 )	129 s	92 s

Table 2: Key performance parameters of JEM-X & OMC Instruments.

	JEM-X	OMC
Energy range	3 keV Ð 35 keV	500 nm Ð 600 nm
Detector	Microstrip Xe/CH4 -gas	CCD + V-filter
	detector (1.5 bar)
Detector area (cm2 )	2 500	CCD: (2061 1056) pixels
		Imaging area: (1024 1024) pixels
Spectral resolution (FWHM)	1.2 keV @ 10 keV	Ð
Field of view (fully coded)	4.8	5 5
Angular resolution (FWHM)	3	23
10 source location (radius)	30	2
Absolute timing accuracy (3 )	122 s	1 s

Figure 3: Spacecraft & Instrument coordinate systems.

Figure 4: The INTEGRAL continuum sensitivities. Time of observation is s, the detection threshold is 3 .