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Дата индексирования: Sat Dec 22 09:45:44 2007
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XMM-Newton Science Analysis System


efftplot (efftplot-2.17) [xmmsas_20070708_1801-7.1.0]

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Description

The bulk of efftplot is powspec, the FTOOLS package which computes the power density spectrum. The parameters of powspec are computed from the parameters of efftplot, such that for each energy band, only one time-averaged PDS is computed. Then for each energy band, efftplot reads the PDS into the FITS file produced by powspec, and plots it with the PGPLOT library. Different PDS can be formatted by adding items related to the observation.

In the PPS, efftplot produces and plots the PDS of the time series measured by EPIC, covering the three energy bands : 0.1 - 2.0, 2.0 - 10.0 and 0.1 - 10.0 keV (The `EPIC FITS source timeseries'). Nevertheless, efftplot can process FITS files with 1 to 6 RATE columns.

The input FITS files contains either total or net count rates, background count rates and the associated errors. The user may also choose whether to use the total or net counts to produce the power density spectrum, via the parameter `bkgsub'. The time series follow a regular binning scheme (i.e. equispaced time bins). The bin width is given by the keyword TIMEDEL which is measured in seconds. The user can also provide a GTI file that has been produced using the SAS task tabgtigen.

First, the task recovers the TIMEDEL keyword, the number of RATE columns in the FITS file (NCOLUMNS) and the number of bins in the light curves (NBINLC). Then, efftplot uses the FTOOLS powspec to compute successive PDS light curves (i.e. each RATE column). At the end of each powspec run, the PDS is saved on disk as a FITS file. The PDS is calculated in data segments of Nbins bins. If the last data segment is incomplete, it is ignored.

The normalization parameter indicates the way in which the PDS is normalized, as follows:

• 0 : PDS is normalized by dividing by the number of bins in each interval (Nbins).
• 1 : PDS is normalized such that the (white) noise level expected corresponds to a power value of 2.
• 2 : PDS is normalized such that its integral gives the squared rms fractional variability (therefore the power spectrum is in units of (rms)**2/Hz). The expected (white) noise level must be subtracted to obtain the rms fractional variability of the series.
• -1 : as =1, but the expected white noise level is subtracted
• -2 : as =2, but the expected white noise level is subtracted. Negative normalization flags should be used only after having established that the observed (white) noise level is as expected. If other normalization flag values are used, they are treated as =0.

When all the lightcurves have been processed, efftplot produces the final postscript file containing all the PDS plots, i.e. the ``EPIC Source FFT plot'' using the PGPLOT library. Finally, the temporary files are deleted.

Among the powspec parameters, the critical ones (e.g. rebintype, nbins, ...) are also efftplot parameters. Of course, many of them have a default value and should not be changed in a PPS run. This default is generally the standard default for powspec. Nevertheless, these default values are explicitly given to powspec by efftplot to avoid possible differences in behavior of the task, depending on the local FTOOLS installation.