XMM-Newton Phase II RPS Users Manual

A..4 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. The input of standard information (target name, catalogued position etc.) in XRPS is trivial. Other input parameters require some more thought:

Choice of prime instrument

The prime instrument is chosen according to the importance of data from either type of XMM-Newton instrument: either EPIC, if imaging with moderate resolution spectroscopy is crucial, or RGS, if the highest possible spectral resolution must be achieved. Let us, for the time being, assume that EPIC is prime.

Science mode of the prime instrument

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

X-ray properties of the source

Based on PIMMS observers can convert ROSAT, ASCA or other known flux and band data (if known), and enter these, together with an X-ray spectral model, e.g. power law, $\Gamma$ = 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.

Duration of observation vs. visibility constraints

Users must check that the requested observation fits into a continuous visibility period of the XMM-Newton orbit, using the XMM-Newton Target Visibility Tool. In case that 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 to 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 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 SPECTROSCOPY mode and OM in the Science User Defined mode with Image and Fast windows.

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 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 orthogonally to each other. For the RGS there must be no source along the dispersion direction of the target spectrum. Such sources must be avoided, which might lead to a position angle constraint.

EPIC filters

Using the instructions provided in the XMM-Newton Users Handbook 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.

RGS readout sequence

The user must determine whether one or several CCDs shall be read out. The whole spectral range (all 8 CCDs) can be read out in 5 s for RGS1 and 10 s for RGS2.

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 25 . If such source should exist, no OM exposure should be included.

OM filters and modes

OM filters and modes have to be chosen according to the optical characteristics of the target (see 5.2.4.5).

Duration of exposures

Normally, 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 § 5.2.4.5 and the OM chapter of the XMM-Newton Users Handbook.