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Spectral Capabilities


The PSPC offers spectral resolution through event pulse heights as well as through the use of the boron filter. Because of the good counter resolution, events occurring in the carbon band can be separated from those at higher energies without significant pulse height smearing. Approximately four different colors can be determined over the whole PSPC band pass. An example of measured PSPC pulse height spectra is given in Figure 10.14 gif; the upper panel contains the extremely soft spectrum of a presumed LMXB in the LMC which is detected only in carbon band; the medium panel shows the pulse height spectrum of an active nearby star with emission both in the C and M bands; while the lower panel shows the pulse spectrum of a cut-off source (LMX-1).

 fig10-1 figure1054

The boron filter allows a further subdivision of the carbon band by comparison of the count rate with and without filter. This filter transmits most of the photons at higher energies while absorbing most photons between 0.18 and 0.28 keV. Therefore the filter/open count rate ratio is sensitive to the spectral intensity between 0.1 and 0.18 keV. For various values of tex2html_wrap_inline2416 we show the filter/open filter ratio versus photon index for power law spectra (Figure 10.15 gif), the filter/open ratio versus temperature for thermal spectra (Figure 10.16 gif), and blackbody spectra (Figure 10.17 gif). In the case of power law spectra the boron filter will be useful for column densities below tex2html_wrap_inline2656  cm tex2html_wrap_inline1930 . For given tex2html_wrap_inline2416 the ratio of filter/open count rate is sensitive to the photon index. For thermal spectra the filter/open ratio is very sensitive to temperature in the temperature range between tex2html_wrap_inline2662  K and tex2html_wrap_inline2528  K while for very high temperatures the filter/open ratio is sensitive to tex2html_wrap_inline2416 . For blackbody spectra the filter/open ratio is rather sensitive to tex2html_wrap_inline2416 for column densities above tex2html_wrap_inline2670  cm tex2html_wrap_inline1930 while for lower column densities the temperature dependence in the range between 0.1 and 0.3 keV is very pronounced.

 fig10-15 figure1070

 fig10-16 figure1075

 fig10-17fig10-1 figure1080

next up previous contents
Next: Positional accuracy Up: FEASIBILITY: XMA+PSPC Previous: Expected Count Rates

Michael Arida
Tue Jun 11 16:18:41 EDT 1996