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Expected Count Rates (in detect cell = 50 of total)

 

 

log(N tex2html_wrap_inline17701 )
kT 0.0 18.0 18.7 19.0 19.7 20.0 20.7 21.0 21.7 22.0
0.01 3.91e-23.76e-23.21e-22.64e-25.94e-31.13e-32.53e-51.00e-9 1.00e-91.00e-9
0.03 1.18e-11.15e-11.04e-19.21e-23.94e-21.77e-26.83e-46.07e-5 1.00e-91.00e-9
0.05 1.69e-11.66e-11.53e-11.40e-17.57e-24.28e-23.42e-34.67e-4 2.10e-61.00e-8
0.10 2.12e-12.09e-11.98e-11.86e-11.21e-18.05e-21.22e-23.50e-3 1.50e-41.82e-5
0.30 2.05e-12.03e-11.96e-11.88e-11.42e-11.10e-14.16e-22.62e-2 6.02e-31.93e-3
0.50 1.98e-11.96e-11.91e-11.85e-11.50e-11.24e-16.51e-24.78e-2 1.48e-25.73e-3
1.00 1.86e-11.85e-11.82e-11.78e-11.53e-11.35e-18.81e-27.06e-2 2.67e-21.17e-2
3.00 1.68e-11.68e-11.65e-11.63e-11.47e-11.35e-19.95e-28.36e-2 3.59e-21.72e-2
5.00 1.63e-11.63e-11.60e-11.58e-11.44e-11.33e-11.01e-18.55e-2 3.77e-21.83e-2
Table 5.10: Thermal bremsstrahlung -- ROSAT HRI energy to count conversion factors (50% of counts)

 

 

log(N tex2html_wrap_inline17703 )
tex2html_wrap_inline17705 0.0 18.0 18.7 19.0 19.7 20.0 20.7 21.0 21.7 22.0
0.0 1.44e-11.43e-11.42e-11.41e-11.32e-11.25e-11.03e-18.93e-2 4.25e-22.17e-2
0.5 1.64e-11.63e-11.61e-11.58e-11.41e-11.29e-19.45e-27.96e-2 3.50e-21.71e-2
1.0 1.81e-11.80e-11.75e-11.70e-11.41e-11.21e-17.52e-26.02e-2 2.42e-21.12e-2
1.5 1.90e-11.90e-11.81e-11.73e-11.32e-11.05e-15.09e-23.79e-2 1.36e-25.97e-3
2.0 1.88e-11.86e-11.77e-11.67e-11.16e-18.50e-23.06e-22.05e-2 6.41e-32.65e-3
2.5 1.78e-11.76e-11.66e-11.54e-19.85e-26.68e-21.75e-21.01e-2 2.67e-31.04e-3
3.0 1.64e-11.61e-11.51e-11.39e-18.20e-25.19e-29.92e-34.76e-3 1.04e-33.74e-4
Table 5.11: Power law -- ROSAT HRI energy to count conversion factors (50% of counts)

 

 

log(N tex2html_wrap_inline17707 )
kT 0.0 18.0 18.7 19.0 19.7 20.0 20.7 21.0 21.7 22.0
0.01 5.17e-14.98e-14.29e-13.56e-18.75e-21.86e-21.59e-5 2.00e-71.00e-91.00e-9
0.03 3.39e-13.28e-12.90e-12.50e-18.41e-22.80e-24.09e-4 3.20e-51.00e-91.00e-9
0.05 2.97e-12.92e-12.73e-12.51e-11.43e-18.16e-25.50e-3 6.24e-42.70e-61.00e-7
0.10 2.74e-12.72e-12.63e-12.52e-11.88e-11.38e-12.54e-2 7.27e-32.69e-42.91e-5
0.30 1.92e-11.92e-11.89e-11.86e-11.68e-11.52e-11.02e-1 7.82e-21.75e-23.95e-3
0.50 2.41e-12.40e-12.38e-12.35e-12.22e-12.12e-11.75e-1 1.47e-14.29e-21.14e-2
1.00 2.27e-12.26e-12.22e-12.17e-11.95e-11.83e-11.51e-1 1.31e-15.33e-22.08e-2
3.00 1.75e-11.74e-11.72e-11.69e-11.54e-11.44e-11.11e-1 9.50e-24.27e-22.05e-2
5.00 1.66e-11.66e-11.64e-11.61e-11.48e-11.38e-11.06e-1 9.07e-24.08e-21.99e-2
Table 5.12: Raymond-Smith -- ROSAT HRI energy to count conversion factors (50% of counts)

 

 

log(N tex2html_wrap_inline17709 )
kT 0.0 18.0 18.7 19.0 19.7 20.0 20.7 21.0 21.7 22.0
0.01 5.59e-25.38e-24.65e-23.88e-29.98e-32.35e-34.80e-6 1.00e-71.00e-91.00e-9
0.03 2.02e-11.98e-11.85e-11.71e-19.85e-25.79e-24.62e-3 5.61e-49.00e-71.00e-9
0.05 2.48e-12.45e-12.35e-12.23e-11.55e-11.08e-11.66e-2 4.00e-37.07e-53.50e-6
0.10 1.89e-11.87e-11.83e-11.78e-11.47e-11.21e-15.07e-2 3.05e-24.40e-39.29e-4
0.30 1.77e-11.77e-11.76e-11.76e-11.71e-11.66e-11.44e-1 1.25e-15.45e-22.52e-2
0.50 1.39e-11.39e-11.39e-11.38e-11.36e-11.34e-11.21e-1 1.09e-15.52e-22.88e-2
1.00 1.04e-11.04e-11.03e-11.03e-11.02e-11.01e-19.29e-2 8.49e-24.72e-22.65e-2
3.00 8.48e-28.48e-28.47e-28.46e-28.38e-28.29e-27.71e-2 7.11e-24.13e-22.41e-2
5.00 8.18e-28.17e-28.17e-28.16e-28.09e-28.00e-27.45e-2 6.88e-24.03e-22.37e-2
Table 5.13: Blackbody -- ROSAT HRI energy to count conversion factors (50% of counts)

The expected HRI count rates depend sensitively on the assumed incident spectrum, which is not well known for many sources. In general, the convolution of the effective area and incident spectrum needs to be calculated to predict the HRI counting rate. Since the effective area is not a simple analytic function, the convolution is not straight-forward. In order to facilitate count rate calculations we provide a series of tables and graphs which give the energy-to-counts conversion factor (ECF) for several spectral models and various spectral parameters. These are based upon the counts collected in a tex2html_wrap_inline17711 detect cell which is assumed to contain 50% of the total source counts that fall on the HRI detector. (Note that other estimation techniques may use the total counts and hence may differ by a factor of two from the results obtained by following the procedures described here.)

Tables for computing the expected count rates in the ROSAT\ HRI were generated for four spectral models. These are:

  1. Thermal Bremsstrahlung (Exponential plus Gaunt Factor) Spectrum (Table 11.2, Figure 11.4 of Appendix F), where kT is in keV.
  2. Power Law Spectrum (Table 11.3, Figure 11.5 of Appendix F), where tex2html_wrap_inline17713 is the energy index.
  3. Raymond-Smith Plasma Spectrum (Table 11.4, Figure 11.6 of Appendix F), where kT is in keV.
  4. Blackbody Spectrum (Table 11.5, Figure 11.7 of Appendix F), where kT is in keV

For each spectral model we calculate the factor by which the unabsorbed source flux (in units of tex2html_wrap_inline17715  erg cm tex2html_wrap_inline17717  s tex2html_wrap_inline17719 ) has to be multiplied in order to obtain the expected HRI on-axis count rate within the tex2html_wrap_inline17721 detect cell. The conversion factor is as a function of the intrinsic source spectrum (characterized by tex2html_wrap_inline17723 or kT), and the interstellar absorption column density tex2html_wrap_inline17725 .

The curves shown in Appendix F Figures 11.4 - 11.7 (or Tables 5.10 - 5.13 reproduced here for convenience) should be used as follows:

  1. Estimate the un absorbed source flux tex2html_wrap_inline17727 (in units of tex2html_wrap_inline17729  ergs cm tex2html_wrap_inline17731  s tex2html_wrap_inline17733 ) in the ROSAT pass band 0.1 - 2.4 keV. This is the flux which would have been incident on the Earth in the absence of any absorption.  
  2. Estimate the interstellar absorption column density.
  3. With the assumed values of tex2html_wrap_inline17735 and spectral parameter ( tex2html_wrap_inline17737 or kT) read from the figures or tables the resulting energy-to-counts conversion factor ECF.
  4. Multiply tex2html_wrap_inline17739 and ECF to obtain the expected ROSAT HRI count rate.

next up previous contents index
Next: Blackbody Spectrum Example Up: 5.3 Feasibility of Observations Previous: Detection of Previously Unknown

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