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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.
Tables for computing the expected count rates in the ROSAT HRI were
generated for four spectral models. These are:
- Thermal Bremsstrahlung (Exponential plus Gaunt Factor) Spectrum
(Table 11.2
, Figure 11.4 ,
where kT is in keV. - Power Law Spectrum (Table 11.3 ,
Figure 11.5 ), where
is the energy index. - Raymond-Smith Plasma Spectrum (Table 11.4 ,
Figure 11.6 ), where kT is in keV.
- Blackbody Spectrum (Table 11.5 ,
Figure 11.7 ), where kT is in keV
For each spectral model we calculate the factor by which the unabsorbed
source flux (in units of 
ergs cm 
s 
) has to be
multiplied in order to obtain the expected HRI on-axis count rate within
the 5'' detect cell as a function of the spectral parameter
( or kT), and the interstellar absorption column density 
.
The curves shown in Figures 11.4 - 11.7
(or Tables 11.2
- 11.5) should
be used as follows:
- Calculate the expected source flux
(in units of
ergs cm s ) in the ROSAT pass band
0.1 - 2.4 keV assuming no interstellar absorption. - Determine the expected interstellar absorption column density.
- With the assumed values of and spectral parameter (
or kT) read from the figures or tables the resulting
energy-to-counts conversion factor ECF.
- Multiply and ECF to obtain the expected ROSAT HRI count rate.
ROSAT HRI Energy to Count Conversion Factors
log(
)
|
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-2 | 3.76e-2 | 3.21e-2 | 2.64e-2 | 5.94e-3 | 1.13e-3 | 2.53e-5 | 1.00e-9 | 1.0
0e-9 | 1.00e-9 |
|
0.03 | 1.18e-1 | 1.15e-1 | 1.04e-1 | 9.21e-2 | 3.94e-2 | 1.77e-2 | 6.83e-4 | 6.07e-5 | 1.0
0e-9 | 1.00e-9 |
|
0.05 | 1.69e-1 | 1.66e-1 | 1.53e-1 | 1.40e-1 | 7.57e-2 | 4.28e-2 | 3.42e-3 | 4.67e-4 | 2.1
0e-6 | 1.00e-8 |
|
0.10 | 2.12e-1 | 2.09e-1 | 1.98e-1 | 1.86e-1 | 1.21e-1 | 8.05e-2 | 1.22e-2 | 3.50e-3 | 1.5
0e-4 | 1.82e-5 |
|
0.30 | 2.05e-1 | 2.03e-1 | 1.96e-1 | 1.88e-1 | 1.42e-1 | 1.10e-1 | 4.16e-2 | 2.62e-2 | 6.0
2e-3 | 1.93e-3 |
|
0.50 | 1.98e-1 | 1.96e-1 | 1.91e-1 | 1.85e-1 | 1.50e-1 | 1.24e-1 | 6.51e-2 | 4.78e-2 | 1.4
8e-2 | 5.73e-3 |
|
1.00 | 1.86e-1 | 1.85e-1 | 1.82e-1 | 1.78e-1 | 1.53e-1 | 1.35e-1 | 8.81e-2 | 7.06e-2 | 2.6
7e-2 | 1.17e-2 |
|
3.00 | 1.68e-1 | 1.68e-1 | 1.65e-1 | 1.63e-1 | 1.47e-1 | 1.35e-1 | 9.95e-2 | 8.36e-2 | 3.5
9e-2 | 1.72e-2 |
|
5.00 | 1.63e-1 | 1.63e-1 | 1.60e-1 | 1.58e-1 | 1.44e-1 | 1.33e-1 | 1.01e-1 | 8.55e-2 | 3.7
7e-2 | 1.83e-2 |
Table: 11.2
Thermal Bremsstrahlung
ROSAT HRI Energy to Count Conversion Factors
log(
)
|
| 0.0 | 18.0 | 18.7 | 19.0 | 19.7 | 20.0 | 20.7 | 21.0 | 21.7 | 22.0 |
| 0.0 | 1.44e-1 | 1.43e-1 | 1.42e-1 | 1.41e-1 | 1.32e-1 | 1.25e-1 | 1.03e-1 | 8.93e-2 | 4.25
e-2 | 2.17e-2 |
|
0.5 | 1.64e-1 | 1.63e-1 | 1.61e-1 | 1.58e-1 | 1.41e-1 | 1.29e-1 | 9.45e-2 | 7.96e-2 | 3.50
e-2 | 1.71e-2 |
|
1.0 | 1.81e-1 | 1.80e-1 | 1.75e-1 | 1.70e-1 | 1.41e-1 | 1.21e-1 | 7.52e-2 | 6.02e-2 | 2.42
e-2 | 1.12e-2 |
|
1.5 | 1.90e-1 | 1.90e-1 | 1.81e-1 | 1.73e-1 | 1.32e-1 | 1.05e-1 | 5.09e-2 | 3.79e-2 | 1.36
e-2 | 5.97e-3 |
|
2.0 | 1.88e-1 | 1.86e-1 | 1.77e-1 | 1.67e-1 | 1.16e-1 | 8.50e-2 | 3.06e-2 | 2.05e-2 | 6.41
e-3 | 2.65e-3 |
|
2.5 | 1.78e-1 | 1.76e-1 | 1.66e-1 | 1.54e-1 | 9.85e-2 | 6.68e-2 | 1.75e-2 | 1.01e-2 | 2.67
e-3 | 1.04e-3 |
|
3.0 | 1.64e-1 | 1.61e-1 | 1.51e-1 | 1.39e-1 | 8.20e-2 | 5.19e-2 | 9.92e-3 | 4.76e-3 | 1.04
e-3 | 3.74e-4 |
Table: 11.3
Power Law
ROSAT HRI Energy to Count Conversion Factors
log(
)
|
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-1 | 4.98e-1 | 4.29e-1 | 3.56e-1 | 8.75e-2 | 1.86e-2 | 1.59e-5 | 2.00e-7 | 1.0
0e-9 | 1.00e-9 |
|
0.03 | 3.39e-1 | 3.28e-1 | 2.90e-1 | 2.50e-1 | 8.41e-2 | 2.80e-2 | 4.09e-4 | 3.20e-5 | 1.0
0e-9 | 1.00e-9 |
|
0.05 | 2.97e-1 | 2.92e-1 | 2.73e-1 | 2.51e-1 | 1.43e-1 | 8.16e-2 | 5.50e-3 | 6.24e-4 | 2.7
0e-6 | 1.00e-7 |
|
0.10 | 2.74e-1 | 2.72e-1 | 2.63e-1 | 2.52e-1 | 1.88e-1 | 1.38e-1 | 2.54e-2 | 7.27e-3 | 2.6
9e-4 | 2.91e-5 |
|
0.30 | 1.92e-1 | 1.92e-1 | 1.89e-1 | 1.86e-1 | 1.68e-1 | 1.52e-1 | 1.02e-1 | 7.82e-2 | 1.7
5e-2 | 3.95e-3 |
|
0.50 | 2.41e-1 | 2.40e-1 | 2.38e-1 | 2.35e-1 | 2.22e-1 | 2.12e-1 | 1.75e-1 | 1.47e-1 | 4.2
9e-2 | 1.14e-2 |
|
1.00 | 2.27e-1 | 2.26e-1 | 2.22e-1 | 2.17e-1 | 1.95e-1 | 1.83e-1 | 1.51e-1 | 1.31e-1 | 5.3
3e-2 | 2.08e-2 |
|
3.00 | 1.75e-1 | 1.74e-1 | 1.72e-1 | 1.69e-1 | 1.54e-1 | 1.44e-1 | 1.11e-1 | 9.50e-2 | 4.2
7e-2 | 2.05e-2 |
|
5.00 | 1.66e-1 | 1.66e-1 | 1.64e-1 | 1.61e-1 | 1.48e-1 | 1.38e-1 | 1.06e-1 | 9.07e-2 | 4.0
8e-2 | 1.99e-2 |
Table: 11.4
Raymond-Smith
ROSAT HRI Energy to Count Conversion Factors
log(
)
|
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-2 | 5.38e-2 | 4.65e-2 | 3.88e-2 | 9.98e-3 | 2.35e-3 | 4.80e-6 | 1.00e-7 | 1.0
0e-9 | 1.00e-9 |
|
0.03 | 2.02e-1 | 1.98e-1 | 1.85e-1 | 1.71e-1 | 9.85e-2 | 5.79e-2 | 4.62e-3 | 5.61e-4 | 9.0
0e-7 | 1.00e-9 |
|
0.05 | 2.48e-1 | 2.45e-1 | 2.35e-1 | 2.23e-1 | 1.55e-1 | 1.08e-1 | 1.66e-2 | 4.00e-3 | 7.0
7e-5 | 3.50e-6 |
|
0.10 | 1.89e-1 | 1.87e-1 | 1.83e-1 | 1.78e-1 | 1.47e-1 | 1.21e-1 | 5.07e-2 | 3.05e-2 | 4.4
0e-3 | 9.29e-4 |
|
0.30 | 1.77e-1 | 1.77e-1 | 1.76e-1 | 1.76e-1 | 1.71e-1 | 1.66e-1 | 1.44e-1 | 1.25e-1 | 5.4
5e-2 | 2.52e-2 |
|
0.50 | 1.39e-1 | 1.39e-1 | 1.39e-1 | 1.38e-1 | 1.36e-1 | 1.34e-1 | 1.21e-1 | 1.09e-1 | 5.5
2e-2 | 2.88e-2 |
|
1.00 | 1.04e-1 | 1.04e-1 | 1.03e-1 | 1.03e-1 | 1.02e-1 | 1.01e-1 | 9.29e-2 | 8.49e-2 | 4.7
2e-2 | 2.65e-2 |
|
3.00 | 8.48e-2 | 8.48e-2 | 8.47e-2 | 8.46e-2 | 8.38e-2 | 8.29e-2 | 7.71e-2 | 7.11e-2 | 4.1
3e-2 | 2.41e-2 |
|
5.00 | 8.18e-2 | 8.17e-2 | 8.17e-2 | 8.16e-2 | 8.09e-2 | 8.00e-2 | 7.45e-2 | 6.88e-2 | 4.0
3e-2 | 2.37e-2 |
Table: 11.5
Blackbody
Next: Examples
Up: FEASIBILITY: XMA + HRI
Previous: Point Source Sensitivity
Michael Arida
Tue Jun 11 16:18:41 EDT 1996