Here we describe the algorithms used for each of the calibration steps:
- Correcting for dead time.
- Computing the true count rates for digital data.
- Computing the true count rates for analog data.
41.3.1 Correcting for Dead Time
The raw counts need to be converted into count rate. The following equation is used to find the count rate.x = (raw counts / sample time)
Where x is the observed count rate.
The following equation is used to correct for dead time.
- y - is the true count rate after deadtime correction.
- x - is the observed count rate.
- t - is the dead time.
41.3.2 Computing the True Count Rate
True count rates for digital data are corrected by using the first equation for a point source and the second for an extended source.
a = (y - pre_amp - darkrate) / (highvolt x pt_effic)
- a - is the final calibrated true count rate for point source.
- b - is the final calibrated true count rate for extended source.
- y - is the true count rate after deadtime correction.
41.3.3 Computing the True Photocurrents
True photocurrents (count rates for analog data) are corrected by the first equation for point sources and the second equation for extended sources.
- c - is the final calibrated true count rate for point source.
- d - is the final calibrated true count rate for extended source.
- n - is the observed digital number.
41.3.4 Calculating Sample Time
The following equation is used to calculate the sample time. The sample time can be found in the data headers under the keyword SAMPTIME.
41.3.5 Calibration Parameter Polynomial
The HSP calibration parameters listed in Table 41.2 are calculated using the following polynomials.X = X0 * [1.0 + a01 * (t - t0) + a02 * (t - t0)2 + a03 * (t - t0)3]
+ [a10 + a11 * (t - t0) + a12 * (t - t0)2 + a13 * (t - t0)3] * (T - T0)
+ [a20 + a21 * (t - t0) + a22 * (t - t0)2 + a23 * (t - t0)3] * (T - T0)2
+ [a30 + a31 * (t - t0) + a32 * (t - t0)2 + a33 * (t - t0)3] * (T - T0)3
- X - is the calibration parameter value.
- X0 - is the base value of the calibration parameter.
- t - is the epoch (time in modified Julian days) of the observation.
- t0 - is the base time.
- T - is the temperature.
- T0 - is the base temperature.
Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved.
Last updated: 01/14/98 16:00:43