XMM RPS Users' Manual

   
Example for an observation of a faint extended source

As an example for a faint extended X-ray source one might consider observing a cluster of galaxies, at relatively low redshift, z. Input of standard information (target name, catalogued position etc.) in XRPS is trivial. Other input parameters require some more thought:

Choice of prime instrument

There might be a cooling flow at the centre. If moderate resolution spectroscopy is most important for the proposed science, the observer might want it to be imaged in the 'aim point' of the EPIC pn camera. Alternatively, if high-resolution spectroscopy is intended, (s)he may want to centre it on the RGS-1 instrument (which is the RGS unit with the highest energy resolution).

Science mode of the prime instrument

If the source is weak, all EPIC cameras can be assumed to have no problems with photon pile-up. In that case, they can all be used in the standard FULL WINDOW imaging mode. RGS could be used in its standard SPECTROSCOPY mode.

Total integration time requirement

Based on PIMMS observers can convert ROSAT, ASCA or other known flux and band data (if known) into the XMM band (0.1-15 keV), and enter these, together with, e.g., X-ray spectral model = Raymond-Smith, kT = 6 keV, N(H) = 3e20 cm^-2 and the lower and upper limit of the energy band over which the X-ray flux was observed into XRPS.

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

Assuming that the cooling flow is located at the core of the cluster, no boresight coordinates need be entered and thus the target coordinates will automatically be propagated into the boresight fields. Otherwise, the boresight would be chosen to be directed towards the location of brightest/most important feature to be observed. 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 expected RGS count rates are lower than those for EPIC. There will thus be no need for fast readouts and RGS would be used in its standard SPECTROSCOPY mode.

Assuming that the cluster fits into the OM's 17' FOV, a default configuration (matching the choice of either EPIC pn or RGS-1 as prime instrument!) would be chosen (``EPIC pn IMG'' or ``RGS 1 IMG'').

EPIC filters

Since the source is assumed to be weak (both in X-rays and the optical/UV) the ``THIN'' optical blocking filter can be used. Observations without any filter might be contaminated by optical radiation (diffuse background or bright optical sources) 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.

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

All X-ray observations of faint sources 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.