XMM-Newton Phase II RPS Users Manual

A..3 Imaging observation of a point source

Users might be interested in observing a bright point source (like, e.g., an unresolved AGN, binary or stellar object). 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 pn, 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 RGS is prime.

Science mode of the prime instrument

RGS can be operated in its standard SPECTROSCOPY mode. In the case where the source has prominent emission lines, the user should be aware of, and check for, potential pile-up problems.

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.

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. Such sources must be avoided, which might lead to a position angle constraint.

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 § 5.2.3).

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 XMM-Newton Users Handbook 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 XMM-Newton Users Handbook account for this).

For MOS we compare the merits of two modes: Small Window Mode ($100\times100$ pixels) is able to accommodate the point source spatially. If the mode is not able to accommodate the expected flux without significant pile-up, then the Timing Mode must be considered.

If no high time resolution is required for the OM observations, an imaging mode default configuration should be chosen (in this case, since RGS is prime instrument, ''RGS Image''). Becasue of the small size of the window it is very important to get the coordinates right.

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

In the case of standard spectroscopy observations there is no need to change anything in the RGS readout sequence. CCDs 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 3 8 9], in which CCD#3 of RGS-1 is read out 4 times more often than all others (assuming that the bright line would be registered on chip#3; see the XMM-Newton Users Handbook section on RFC arrays ). If the mode is not able to accommodate the expected flux without significant pile-up, then the Small Window mode must be considered.

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