XMM RPS Users' Manual

   
Timing observation of a variable source

Consider observing a bright point source, as above (like, e.g., an unresolved AGN, binary or stellar object), but now with a special interest in high time resolution measurements. In addition to trivial input like, e.g., target name, catalogued position, etc., input parameters to be chosen are:

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 grism observations with simultaneous flux monitoring via a fast mode window covering the zero-order image are mandatory. Let us, for the time being, assume that EPIC pn is prime.

Science mode of the prime instrument

For high time-resolution observations the EPIC pn TIMING mode is a suitable choice.

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.

Science modes of the other instruments

Based on the nature of the example, one can assume that all instruments will be operated in their fast modes. EPIC pn reaches a time resolution of 0.03 ms in its TIMING mode, MOS reaches a resolution of 1.5 ms. Note that the pn camera in its Small Partial Window mode already reaches a time resolution of 6 ms, which would at the same time render possible imaging of the target. RGS would be operated in the HIGH TIME RESOLUTION mode and OM in the fast mode default configuration EPIC pn IMG FST.

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. In particular when the EPIC TIMING mode and also the RGS HIGH TIME RESOLUTION mode is used, one must ensure that nearby sources do not contaminate the target data. There must be no nearby source in the same column of the EPIC cameras as the science target. However, note that the two MOS cameras are mounted orthogonal to each other. For the RGS there must be no source along the dispersion direction of the target spectrum. If any such sources should exist and must be avoided, this might lead to a position angle constraint (which in turn makes the observation ``fixed'' in time).

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

The user must determine whether one single CCD (if yes, which one) or all nine RGS CCDs shall be read out. The whole spectral range (all 9 CCDs) can be read out in about 150 ms.

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

Targets with extremely high count rates might lead to very high telemetry rates. The limits listed in the UHB section on EPIC modes apply. If these are not exceeded, 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.