XMM RPS Users' Manual

   
Imaging observation of a point source

Many users might be interested in observing a bright point source (like, e.g., an unresolved AGN, binary or stellar object). In addition to trivial input like, e.g., target name, catalogued position, etc., some more input parameters must be chosen:

Choice of prime instrument

The prime instrument is chosen according to the importance of data from either type of XMM instrument: either EPIC pn, if imaging with moderate resolution spectroscopy is crucial, or RGS-1, if the highest possible spectral resolution must be achieved, or even OM, if simultaneous optical/UV fast mode data are mandatory. Let us, for the time being, assume that RGS-1 is prime.

Science mode of the prime instrument

Depending on the required science data (either standard spectroscopy or high time-resolution spectro-photometry), RGS can be operated either in its standard SPECTROSCOPY or the HIGH TIME RESOLUTION mode. In case SPECTROSCOPY is used and if the source has prominent emission lines, SciSim modeling of the spectrum should be performed to check for potential pile-up problems.

Total integration time requirement

Based on PIMMS observers can convert ROSAT, ASCA or other known flux and band data (if known), and enter these, together with, e.g., X-ray spectral model = power law, $\alpha_E$ = 0.7, N(H) = 3e21 cm^-2 and the lower and upper limit of the energy band over which the X-ray flux was observed.

Length of observation vs. visibility constraints

Users must check that the requested observation fits into a continuous visibility period of the XMM orbit, using the XMM Target Visibility Tool. In case the required total integration time is longer than the longest possible visibility window, the observation must be split into an adequate number of individual observations.

Pointing coordinates

No boresight coordinates need be entered to centre the target on the prime instrument, because the target coordinates will be propagated automatically into the boresight fields, if no other values are provided. The best data quality will be achieved in the aim point of the prime instrument.

Avoidance of nearby bright sources

Optical and X-ray catalogues should be searched for nearby bright sources which might lead to contamination of either the X-ray (e.g., RGS spectral overlaps) and/or optical/UV observations. If any such sources exist and must be avoided, this might lead to a position angle constraint (which in turn makes the observation ``fixed'' in time).

Science modes of the other instruments

The science modes of the instruments will mostly be determined by the level of photon pile-up to be expected. As mentioned above (in § 5.3.2), EPIC pile-up calculations should be oriented at the brightest emission region's count rate. In the case of a bright knot in a known SNR, this could be done by estimating from (for example) ROSAT images the brightness within one XMM Point-Spread Function (PSF; see UHB section on XMM X-ray PSF ). For the PSF a Full Width at Half Maximum (FWHM) of 6'' can be assumed.

For the pn camera we decide that the Small Window Mode is necessary to accommodate the source brightness without pile-up degradation (using the information provided in the UHB section on EPIC modes ). This mode offers a total of 4' field coverage. We note the effect of significant dead time, which must be taken into account to obtain the correct exposure time (PIMMS and the plots provided in the UHB account for this).

For MOS we compare the merits of two modes: Partial Window Mode ( $100\times100$ pixels) is able to accommodate the point source spatially, although consideration should be given then to using the MOS as prime instrument to ensure minimal pointing acquisition errors. If the mode is not able to accommodate the expected flux without significant pile-up, then the Timing Mode must be considered.

The expected RGS count rates are lower than those for EPIC. Therefore, RGS can in most cases be operated in its SPECTROSCOPY mode.

If no high time resolution is required for the OM observations, an imaging mode default configuration should be chosen (in this case, since RGS-1 is prime instrument, RGS 1 IMG). For parallel fast mode optical/UV monitoring, the RGS 1 IMG FST default configuration should be chosen.

EPIC filters

Using the instructions provided in the UHB on EPIC filters , the user must decide which optical blocking filter suppresses optical loading in the soft part of the X-ray passband sufficiently and at the same time has minimal impact on the proposed science. Observations without any filter, especially of bright sources, should not be conducted, because they will be contaminated by optical radiation compromising the accuracy of the EPIC energy calibration.

RGS readout sequence

In case of standard spectroscopy observations there is no need to change anything in the RGS readout sequence. CCDs 1-9 will then be read out sequentially. However, there might be strong emission lines that the user wants read out faster than the rest of the spectrum. One way of doing this would be to use the RGS SPECTROSCOPY mode and a readout sequence of, e.g. [3 1 2 3 4 5 3 6 7 3 8 9], in which CCD#3 is read out 4 times more often than all others (assuming that the bright line would be registered on chip#3; see the UHB section on RFC arrays ). In case the HIGH TIME RESOLUTION mode should be chosen, the user must determine whether one single CCD or all nine RGS CCDs shall be read out.

OM brightness limit

Before planning details of OM observations, users should check for the presence of bright optical/UV sources within the OM's FOV. There should be no source in the FOV that violates the brightness constraints tabulated in UHB Table 19 . If any such source should exist (and it cannot be avoided by, e.g., reducing the OM FOV by using the magnifier as optical element), the OM MUST be put in the ``GO-OFF'' mode (which corresponds to the blocked filter position) to protect it from radiation damage.

OM filters

If the observer has no particular interest in specific wavelength ranges, the recommended OM filters (as listed in the UHB section on OM default configurations ) should be chosen.

Length of exposures

Normally the X-ray observations can be obtained in a single exposure covering the entire duration of the observation.

The OM exposure times should be chosen according to the explanations in § 5.3.3.5 and the OM chapter of the UHB. An example for how OM default configurations work is shown above, in § 3.3.