XMM-Newton Phase II RPS Users Manual

A..2 Observation of a bright extended source

Consider as an example for a bright extended X-ray source a relatively compact supernova remnant (SNR). 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

There might be a bright emission knot near the desired field centre. If moderate resolution spectroscopy is most important for the proposed science, the observer might want to select the EPIC pn camera. Alternatively, if high-resolution spectroscopy is intended, they may want to chose the RGS instruments (which is the unit with the highest energy resolution). Let us, for the time being, assume that RGS is prime.

Science mode of the prime instrument

RGS can probably be used in its standard SPECTROSCOPY mode. In case of doubt, i.e., if the source has prominent emission lines, the user should 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. thermal bremsstrahlung, kT = 5 keV, N(H) = 1e20 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 by 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

Assuming that the bright knot is not located at the centre of the SNR, its coordinates must be entered into the boresight fields. This is the position on which the prime instrument will be centred. 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), EPIC pile-up calculations should be based on 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-Newton Point-Spread Function (PSF; see XMM-Newton Users Handbook section on XMM-Newton X-ray PSF ). For the PSF a Full Width at Half Maximum (FWHM) of $6''$ can be assumed.

For the pn camera we compare the merits of two modes: Full Frame Mode could be used if the pile-up constraints are acceptable for the science goals. Large Window Mode can be used for sources up to $15'$ extent, and where exterior to this range there are no bright regions that would affect the desired image.

For MOS we compare the merits of two modes as well: Full Frame Mode could be used if the pile-up constraints are acceptable for science goals. The Large Window ($300\times300$ pixels) can be used for sources up to $6'$ extent.

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 is prime instrument, ''RGS Image''). The optical surface brightness of the brightest region of the target must be compared with the OM brightness limits (UHB Table 25 ).

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. The CCDs will then be read out sequentially. However, there might be strong emission lines, which the user wants to 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 ).

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 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

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. For the OM imaging mode each exposure must have a duration of 800-5000 s.