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Suggested method for dealing with telemetry overflow

Occasionally, the intensity of bright sources is such that the register storing the detected count rate overflows before telemetry (the register holds a maximum of 255 counts before telemetry). This can often be corrected after examining each PHA spectrum. An example is shown in the upper panel of figure 2 .

In this example count rates from pulse height channels 5 and 6 are obviously affected by overflow. The light curve from one of these channels is shown in the lower panel of figure 2. The data can be corrected by the following procedure. Sort the data at maximum time resolution (2 seconds in this example), but do not perform the corrections for deadtime (run sortac with the parameter GNG_DEAD_CORR set "No" ). Obviously, the time bins whose count rate is below 200 counts sec-1 have to be corrected. This is achieved by adding 512 counts sec-1 (= 256 counts) to the count rate in the affected time bins (the variance array must be corrected as well). The program correct_data performs this correction automatically for one PHA channel; an example of this program is given below:

qcl>correct_data
 
** CORRECT_DATA Version 1.3 Wed Sep 10 22:28:26 1997 **
 
FDG_NCUBE Number of data files to fudge = 0 =1
FDG_DATIN001 Data filenames =gx339_88a.cube
FDG_IDLO First ident to correct = 1 =1
FDG_IDLO Last ident to correct = 2 =2
FDG_IPHA PHA Channel to correct = 1 =6
FDG_CRATE Maximum count-rate to be corrected = 0.0 =200.0
Data needs correcting......
Data needs correcting......
qcl>

The data are then corrected for deadtime using the program deadtime; an example of its use is given below:

qcl>deadtime

** DEADTIME Version 1.1 Tue Aug 19 19:48:46 1997 **
 
DTM_NCUBES Number of data files to check = 0 =1
DTM_DATIN001 Input data file names =gx339_88a.cube
Correcting data for deadtime......
qcl>

The program deadtime corrects data taken in MPC1, MPC2 and MPC3 modes. Note that the program deadtime is only required if the register storing the detected count rate overflows before telemetry; the program sortac will performed the deadtime correction for non-overflow data.


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