XMM Users' Handbook

   
Basic characteristics

The most important characteristics of XMM are compiled in Table 1. More detailed numbers will follow in the chapters on the individual instruments (below) and a comparison with other X-ray satellites is provided in § 3.7. The basic characteristics of XMM are:

 

Table 1: XMM characteristics - an overview

Instrument	EPIC MOS	EPIC pn	RGS	OM
Bandpass	0.1-15 keV	0.1-15 keV	0.35-2.5 keV1	160-600 nm
Orbital target vis.2	5-145 ks	5-145 ks	5-145 ks	5-145 ks
Sensitivity3	$\sim10^{-14~(4)}$	$\sim10^{-14~(4)}$	$\sim8\times10^{-5~~(15)}$	24 mag13
Field of view (FOV)	30' 5	30' 5	$\sim 5'$	17' 6
PSF ( FWHM/HEW)7	6''/15''	6''/15''	N/A	$\sim1''$
Pixel size	40 $\mu$m (1.1'')	150 $\mu$m (4.1'')	81 $\mu$m ( $9\times10^{-3}$ Å)14	0.5'' 8
Timing resolution9	1 ms	0.03 ms	16 ms	50 ms
Spectral resolution10	57 eV	67 eV	0.04/0.025 Å11	0.5/1.0 nm12

Notes to Table 1:
1) In the -1. grating order (wavelength range: 5-35 Å; $\lambda$ [Å] $\times$ E [keV] = 12.3984).
2) Total visibility per orbit; minimum of 5 ks in order to ensure observatory efficiency. Maximum continuous visibility is ca. 70 ks.
3) After 10 ks; cf. overview tables on the individual instruments.
4) In the range 0.1-15.0 keV, in units of erg s^-1 cm^-2, see § 3.3.9 for details.
5) See Fig. 15 for the detailed shape of the FOV.
6) Maximum window size that can be read out at a time: $8'\times8'$.
7) See Fig. 4 for a ground-calibraton point source measurement.
8) 1'' with default $2\times2$ binning. A higher resolution is achieved with the OM magnifier.
9) In the fastest data acquisition mode (i.e., fast mode for OM and EPIC, high time resolution mode for RGS, reading out only one of nine CCDs).
10) At 1 keV energy. At the energy of Fe K$\alpha$ (6.4 keV), the energy resolution of both EPIC cameras is ca. 130 eV.
11) In -1. and -2. order, resp.; at 1 keV, this corresponds to 3.2/2.0 eV (HEW).
12) With grism1 (UV) and grism2 (optical), respectively.
13) For a 1000 s white light filter observation of a B0 star; dependent on pointing direction (celestial background).
14) In spectroscopy mode (standard $3\times3$ pixel on-chip binning applied).
15) OVII 0.57 keV line flux in photons cm^-2 s^-1, for an integration time of 10 ks and a background of 10^-4 photons cm^-2 s^-1 keV^-1. More details are provided in § 3.4.5.

• Simultaneous operation of all science instruments

  If not prohibited by target brightness constraints, all six XMM science instruments operate simultaneously. They work independently (i.e., exposures of the individual instruments do not necessarily start and end at the same time).

• High sensitivity

  XMM carries the X-ray telescopes with the largest effective area of a focussing telescope ever: the total mirror geometric effective area at 1 keV energy is ca. 1550 cm² for each telescope, i.e., 4650 cm² in total.

• Good angular resolution

  XMM's high sensitivity is achieved by using 58 thin nested mirror shells in each X-ray telescope. The achieved point-spread function (PSF) has a full width at half maximum (FWHM) on the order of 6'' and a HEW, at which 50% of the total energy are encircled, of ca. 15''.

• Moderate and high spectral resolution

  The EPIC CCD cameras have moderate spectral resolution (with a resolving power, E/$\Delta$E, of ca. 20-50). The RGS spectrometers offer much higher spectral resolution, with a resolving power in the range of 200-800.

• Simultaneous optical/UV observations

  Observations with the co-aligned OM optical/UV telescope render possible the monitoring and identification of X-ray sources seen by the X-ray telescopes as well as imaging of the surrounding field.

• Long continuous target visibility

  A highly elliptical orbit offers continuous target visibility of up to more than 40 hours, with a minimum height for science observations of 40,000 km. This is very favourable for studies of source variability and also in order to achieve a high overall observatory efficiency. Due to the required off time near perigee and the telemetry gap near apogee, combined with the absence of onboard data storage devices, these 40 hours will be split into two visibility periods of ca. 70 ks each, with a short gap (of order one hour) in between.

For a comparison of these basic characteristics with those of other past or contemporaneous X-ray satellite missions, see § 3.7.

More detailed information on the mirrors and on the instruments listed in Table 1 and their observing modes is provided in the following sections (§§ 3.2-3.5).