XMM Users' Handbook

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Next: EPIC photon pile-up Up: EUROPEAN PHOTON IMAGING CAMERA Previous: Imaging effective area

   
EPIC's sensitivity limits

The EPIC sensitivity limits depend on the angular structure and the spectral characteristics of the source that is observed. The numbers for an unresolved point source with a power law emission spectrum are listed in Table 5.


 
Table 5: 5-$\sigma $ point source sensitivity of the EPIC pn camera1
Int. time [ks] 0.1-2.4 keV 0.4-4.5 keV 2-10 keV 0.1-15 keV
10 17 20 64 33
20 9 11 33 18
30 7 8 20 13
60 4 5 13 8
100 2.7 3.5 8.7 5.7
Notes to Table 5:
1) All fluxes are in units of [10-15 erg cm-2 s-1], for an $\alpha _E$ = 0.7 power law spectrum, assuming only extragalactic X-ray background radiation (as described in § 3.3.7).

Both internal (particle-induced) and external (celestial X-ray) background was included in the calculations, as described in § 3.3.7. A detect cell the size of the FWHM of the XMM PSF were used.


 
Table 6: EPIC pn OVII 0.57 keV line sensitivity1
Cont. flux2 10 ks 100 ks
10-3 103 32.2
10-4 33.6 10.3
10-5 11.8 3.36
10-6 5.07 1.18
10-7 3.35 0.51
10-8 3.08 0.34
10-9 3.05 0.31
Notes to Table 6:
1) All line fluxes are in units of [photons cm-2 s-1].
2) In [10-6 photons cm-2 s-1 keV-1].


 
Table 7: EPIC pn FeXXV 6.63 keV line sensitivity1
Cont. flux2 10 ks 100 ks
10-3 82.3 25.7
10-4 27.1 8.23
10-5 9.79 2.71
10-6 4.56 0.98
10-7 3.32 0.46
10-8 3.15 0.33
10-9 3.13 0.31
Notes to Table 7:
1) All line fluxes are in units of [photons cm-2 s-1].
2) In [10-6 photons cm-2 s-1 keV-1].

The sensitivity limits for two selected emission lines are tabulated in Tables 6 and 7. Here the background was treated as if it were part of the underlying continuum flux. In Tables 5-7 and Figs. 24-26 the sensitivity limits of only the EPIC pn camera are provided. Using the effective area curves from above, one can estimate that the numbers should be multiplied by a factor of 0.75 to obtain the approximate sensitivity of all EPIC cameras combined.

Fig. 24 displays the minimum detectable source flux for a point source with an $\alpha _E$ = 0.7 power law spectrum, Fig. 25 that of an $\alpha _E$ = 3.0 (``soft excess'') source. Fig. 26 shows the minimum detectable source flux for 30'' extended sources with a kT = 0.3 keV Mewe-Kaastra-Liedahl (in the following ``Mekal'') thermal plasma.


  
Figure 24: EPIC pn sensitivity limits for a point source with an $\alpha _E$ = 0.7 power law spectrum, for different energy bands, see Table 5.
\begin{figure} \begin{center} \leavevmode \epsfig{width=0.6\hsize, angle=270, file=figs/epic_limit_17.eps} \end{center} \end{figure}


  
Figure 25: EPIC pn sensitivity limits for a point source with an $\alpha _E$ = 3.0 power law spectrum, for different energy bands, see Table 5.
\begin{figure} \begin{center} \leavevmode \epsfig{width=0.6\hsize, angle=270, file=figs/epic_limit_40.eps} \end{center} \end{figure}


  
Figure 26: EPIC pn sensitivity limits for a 30'' extended source with a kT = 0.3 keV Mekal thermal plasma spectrum.
\begin{figure} \begin{center} \leavevmode \epsfig{width=0.6\hsize, angle=270, file=figs/epic_limit_ext.eps} \end{center} \end{figure}

next up previous contents
Next: EPIC photon pile-up Up: EUROPEAN PHOTON IMAGING CAMERA Previous: Imaging effective area
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