XMM Users' Handbook

   
OPTICAL MONITOR (OM)

Principal Investigator: Prof. K. O. Mason, Mullard Space Science Laboratory

Besides its three X-ray telescopes, XMM also has a co-aligned 30-cm optical/UV telescope (OM), providing for the first time the possibility to observe simultaneously in the X-ray and optical/UV regime from a single platform. A summary of OM's salient properties is provided in Tab. 12. Although small in size, the OM is a powerful instrument because of the absence of atmospheric extinction, diffraction and background. It can obtain simultaneous optical/UV observations of sources in the field of view in the waveband from 160 to 600 nm. Imaging over the central part of the X-ray field of view with a resolution of ca. 1'' (depending on instrument configuration), low-resolution grism spectra of X-ray sources or high time-resolution photometry can be obtained. Due to the extreme sensitivity of its detectors, the OM cannot be used for observations of optically bright sources ($m_V \leq$ ca. 10 mag).

 

Table 12: OM characteristics - an overview

Total bandwidth1	160 - 600 nm
Spectral bandwidth2	160 - 550 nm
Sensitivity limit3	24 mag
Field of view	ca. 17' 4
PSF ( FWHM)	ca. 1''
Timing resolution5	50 ms
Spectral resolution6	0.5/1.0 nm
Brightness limit7	mV = 10 mag

Notes to Table 12:
1) See Fig. 69 for filter bandpasses.
2) Covered by two grisms.
3) For a 1000 s white light observation of a B0 star; see Table 16 for expected integration times on three stellar types.
4) Maximum observable FOV per exposure due to onboard memory constraints: ca. $8'\times8'$ (cf. § 3.5.9.2).
5) In the fast mode.
6) With the UV and optical grism, respectively.
7) For an A0 star with the V filter; see Tab. 19.