XMM Users' Handbook

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XMM EPIC vs. AXAF ACIS-I pile-up comparison

It has been shown above (§ 3.3.10) how pile-up affects the accuracy of spectral fits and the shape of the X-ray PSF. Figs. 76 and 77 show the fraction of piled-up events for different numbers of counts per CCD frame (in full window imaging mode). One can see in Fig. 77 that pile-up effects for given source fluxes are more severe for ACIS-I by more than an order of magnitude compared to EPIC MOS and even by two orders of magnitude compared to EPIC pn.


  
Figure 76: Comparison of AXAF ACIS-I vs. XMM EPIC (pn and MOS) pile-up for different total frame count rates. The frame times are 3.3, 2.8 and 0.07 seconds for ACIS-I, MOS and pn, respectively.
\begin{figure} \begin{center} \leavevmode \epsfig{width=0.8\hsize, file=figs/Pile-up_2.ps} \end{center} \end{figure}


  
Figure 77: Comparison of AXAF ACIS-I vs. XMM EPIC (pn and MOS) pile-up for different incident source fluxes, after conversion of counts per frame to flux units, adopting an $\alpha = -1.7$ power law spectrum with an absorbing hydrogen column density of $3\times 10^{20}$ cm-2.
\begin{figure} \begin{center} \leavevmode \epsfig{width=0.8\hsize, file=figs/Pile-up_5.ps} \end{center} \end{figure}

next up previous contents
Next: Observing with XMM Up: A comparison of XMM Previous: Non-dispersive spectroscopy: an example
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