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Purpose: To estimate the number of residual afterpulse events in an
image (afterpulse events only affect the R1 and R1L bands). Those
afterpulse events associated with X-ray events can be
eliminated by excluding all events occurring within 0.35 ms of a preceeding
event. FIT_AP is a method to estimate the remaining AP events. FIT_AP
models the 1/4 keV pulse-height distribution with the following components:
1) a fixed particle background component determined by scaling a nominal
spectrum by the total number of particle background counts reported by
CAST_PART, 2) a fixed scattered solar X-ray background determined by
scaling a nominal spectrum by the total number of particle background
counts reported by TILT, 3) a thermal component whose temperature is
varied by the user and whose normalization is fit by the program, this is
the only component which is folded through the detector response matrix and
effective areas, and 4) an afterpulse pulse-height distribution whose shape
is taken from the excluded events (those within 0.35 ms of a preceeding
event) and whose normalization is fit by the program. This fitted
normalization is an estimate for the number of afterpulse events.
Note that the number of afterpulse counts (an output of this program) is needed for the program CAST_PART and that the result of CAST_PART is needed as an input to this program. This circular relationship is resolved simply by running CAST_PART first with zero for the afterpulse input, and killing the program after it produces the value for the total number of particle background counts. FIT_AP can then be run to determine the number of afterpulse events, which can then be fed back to CAST_PART.
1) Observation data set fits files - none
2) Other fixed input - SSX.DAT nominal scattered solar X-ray spectrum, PART.DAT nominal particle background spectrum, spec.dat output from the program CAST_DATA containing the selected afterpulse pulse-height distribution and the accepted even pulse-height distribution, DRM.FITS detector response matrix, EFF_AREA.DAT on-axis effective areas, WINDOW.DAT window transmission, GAS_EFF.DAT PSPC counter gas stopping efficiencies, and RSPECTRA.FITS Raymond and Smith (1991 vintage) thermal spectra.
1) Number of particle background events - taken from the output of program CAST_PART.
2) Number of scattered solar X-ray events - taken from the output of program TILT.
3) Pulse-height range to fit - lower limit of 8 or 11 depending on whether the data were collected at high or low gain, upper limit of 30.
4-?) Temperature of thermal spectrum - spectrum used to model the 1/4 keV pulse-height distribution. This is repeated until the best fit (as opposed to a good fit, the values will in general be poor) is achieved. The temperature should be in the range 5.9 - 6.2.
The program lists the values for the fitted AP parameter along with the statistics.
A QDP plot file, plot_ap.qdp, is created.