XMM-Newton Science Analysis System: Users' Guide

4.7.1 How to analyse a piled-up Timing mode observation

If the source count rate is greater than $\sim800$counts/s for a pn Timing mode observation or $\sim100$counts/s for MOS Timing mode then the source events are likely to be affected by photon pile-up.

This can be checked by selecting events from regions which exclude the inner column(s) of the data and running epatplot. For instance the spatial selection region, which shows no pile-up for the MOS may be:

( RAWX in [280:298] || RAWX in [303:321] )

The BACKSCAL value can be calculated for the created spectrum in the normal manner using xmmselect or the backscale task. Similarly the task rmfgen may be used to create the redistribution matrix (RMF) in the normal manner (see § 4.10.2).

The calculation of the ARF is a little more complicated because the encircled energy (PSF) correction is not performed correctly by arfgen in this case. To overcome this problem the following steps need to be taken.

1. Produce a spectrum (spec_full.ds) from the full area without excluding the central columns, e.g. ( RAWX in [280:321] )

2. Produce a spectrum (spec_inner.ds) from the excluded region, e.g.

   ( RAWX in [299:302] )

3. Produce an ARF for both of these files

   arfgen spectrumset=spec_full.ds arfset=arf_full.ds
   arfgen spectrumset=spec_inner.ds arfset=arf_inner.ds

4. Subtract the inner ARF from the total ARF by using the ftool:

   addarf "arf_full.ds arf_inner.ds" "1.0 -1.0" arf_outer.ds

The arf_outer.ds file can then be used as the ARF for fitting the spectrum created from the region:

( RAWX in [280:298] || RAWX in [303:321] )

together with the RMF produced earlier.