|Z Cha||85/186||Nova Vul||85/162||H1622-751||85/070|
|Delta Tra||85/070||AM Cvn||85/155||Error Box||85/154|
|Error Box||35/149||1053+70||84/326||Beta Hyd||84/266|
*except for Detector C.
3. Separate positive and negative offset difference spectra are supplied.
Examination of Figures 2 (positive offset) and 3 (negative offset) suggests that
there are small differences between them.
The spectra have been smoothed using a 7 point weighted
average as before but the Argon spectra have not had the counts in channel
numbers 8 set to zero as before since we were hopeful that the stricter checks
for the presence of weak sources would enable a reliable estimate of the shape of
the spectra in these channels to be made. However, examination of the count rates
obtained before and after array swaps in a number of Abell cluster
observations where the source is not expected to vary suggest that it is better
to set the count rates in Argon channel numbers 8 to zero as before. This has not
been done on the files on the calibration update tape and is left to the
individual user. in addition it is not clear whether the observed difference
spectra for the corner detectors (A,D,E and H) which are very smalI are merely
the result of fluctuations in the background and should be set to zero.
In general it is always better to generate a set of individual difference spectra for an observation of interest if at all possible. This can easily be done if data exists for both half arrays in a positive and negative offset direction by subtracting the -ive from the +ive spectrum and dividing the counts in the resulting spectrum by 2. This of course, assumes that the shape and magnitude of the difference spectra are the same in the two directions which is probably OK to first order (see Figures 2 and 3).
Alternatively, if only 1 array swap is present the two sets of slew data can be used to estimate the difference spectra. In this case the resulting difference spectra can be quite noisy and can more successfully be used -to normalise the intensity of the standard difference spectra.
The layout of the new difference spectra on the calibration update tape is:
1 Argon detector 1 Positive offset diff. spectrum
2 Argon detector 1 Negative offset diff. spectrum
3 Argon detector 2 Positive " " 4 Argon detector 2 Negative " " . 16 Argon detector 8 Negative " " 17 Argon Half 1 (1-4) Positive " " 18 Argon Negative " " 19 Argon Half 2 (5-8) Positive " " 20 Argon Half Negative " " 21-40 As above for the Xenon detectors
Where a record is 128 words. The values read from the tape should be multiplied by 10-5 to obtain cts/s/bin as with the original difference spectra on the CCF and are for channels 1 through 128 where channel 1 of the Argon detectors is always zero. Note that the supplied spectra are deadtime correction. In order to correct a background spectrum obtained in an offset configuration the relevant difference spectrum shjould be added if the background spectrum was obtained in a negative offset direction and subtracted if the offset spectrum was obtained in a positive offset direction.