If any window is required during the analysis, a window file containing the relevant windows must be created with the xronwin task, before running a XRONOS task. The file may then be given as the value for the window parameter.
Time and Phase windows are applied to Bins. Only those bins whose center time is within the start and stop of a time window or phase window (for a specified epoch and period) are accepted.
Intensity and Exposure Windows can be specified independently for: (i) Bins , (ii) New Bins , (iii) Intervals (applied in the given order). When dealing with more than one time series, Intensity and Exposure Windows must be specified separately for each series.
Time Windows consist of up to 1000 start/stop times. Only those bins whose center time is within the start and stop times of a time window are accepted. Time Windows must be chronologically ordered.
Time windows may be specified in several formats, all of which will be automatically recognized by the xronwin task:
* d = days ........................... e.g. 123.524268391 * d s = day and sec .................. e.g. 123 45296.789 * d h m s ms = day hr min sec msec ... e.g. 123 12 34 56 789
Time windows covering a larger duration than the input series are reset to the start and stop of the input series. The first interval can be forced to start at the start time of the first time window by specifying the hidden parameter, forcestart=yes, when executing the primary XRONOS tasks: autocor, crosscor, efold, efsearch, lcstats, lcurve, powspec, and timeskew.
NOTE, WHEN TIME WINDOWS ARE SET IN THE WINDOW FILE: The time used within XRONOS tasks is Truncated Julian Days (TJD= JD-2440000.5) if either (1) the keyword MJDREF is present in the header or (2) if the TIMESYS value is one of the following strings MJD or JD or TJD. If (2), the time values are expected to be stored as JD, MJD or TJD in the header keywords and in the TIME column in which case the MJDREF keyword is not used (it should not be present). When Time windows are set using xronwin, they must be compatible with the values in header of the timing keywords and/or the values in the TIME column.
Phase Windows consist of an Epoch, a Period, and up to 10 start and stop Phases. Only those bins whose center time is within the specified start and stop phases (for the specified epoch and period) are accepted. Phases range from 0 to 1. Phase Windows must be phase ordered (except for the case in which the last window straddles phase 0).
The Epoch may be specified in several formats, all of which will be automatically recognized by the xronwin task:
* d = day ............................ e.g. 123.524268391 * d s = day and sec .................. e.g. 123 45296.789 * d h m s ms = day hr min sec msec ... e.g. 123 12 34 56 789Two formats are available to specify the Period:
* D = day ............................ e.g. 0.1234567 * S = sec ............................ e.g. 10666.659
Intensity Windows consist of a set of up to 10 minimum and maximum intensity levels. Units are the same as in input files (counts/s usually). Intensity windows must be ordered with increasing intensity and can be specified independently for the intensity of (i) Bins, (ii) Newbins, (iii) Intervals, for each of the series which is being analysed. Note that the "intensity" of an interval is its average intensity. Only those Bins, Newbins, and Intervals whose intensity is within the corresponding specified minimum and maximum intensities will be accepted.
Intensity windows in newbins can be used in conjunction with "Special Newbin Windows". Special Newbin Windows are used to exclude the parts of a light curve which immediately follow or precede a burst or a background event which has been rejected by intensity windows in newbins. The Special Window operates on newbins in conjunction with intensity windows (in newbins) and are specified by changing to positive values the parameters spwinbefore and spwindowafter. Their use is the following: if e.g. spwinbefore=10, all newbins, whose center time is within 10 second before the center time of a newbin rejected by intensity windows, will also be rejected; if e.g. spwindowafter=20, all newbins, whose center time is within 20 second after the center time of a newbin rejected by intensity windows, will also be rejected.
Exposure Windows consist of a minimum and a maximum exposure level. Units are such that 1 means 100% exposure. Exposure windows can be specified independently for the exposure of (i) Bins, (ii) Newbins, (iii) Intervals, for each of the series which is being analysed.
Note that the Bin Exposure used by XRONOS tasks, besides dead time includes also instrument-dependent constants (i.e. the collimator efficiency for the ME and GS, the normalisation for the LE) such that, when dealing with photon counting experiments, the relevant Poisson statistics can be reconstructed. For example if a 5 s bin in an input file has been effectively "exposed" only for 2 s (e.g. as a consequence of dead time effects, collimator efficiencies, data dropouts etc.), then its exposure is 40%.
The Newbin Exposure is obtained by propagating the bin exposures to each newbin; for example, if in a 30 s newbin the total exposure (due to the sum of the individual exposure of the bins contributing to the given newbin) is 18 s then its exposure is 60%.
The Interval Exposure is the ratio of accepted to expected newbins: for example, if a 128 newbin long interval contains only 32 accepted newbins, then its exposure is 25%.
Note that exposures can be higher than 100% (e.g. if the newbin time is not a multiple of the bin time, then "beats" are generated which might bring the exposure of a newbin to values 100%; or if two or more input files for the same time series overlap in part, some of the newbins will be more than 100% exposed).
Default exposure windows are used in many XRONOS tasks, primarily to avoid analysing data sets which are too inhomogeneous with respect to their statistical properties. The default exposure windows are:
NOTE: The minimum default Exposure windows in an Interval is ignored in lcurve, efold, and efsearch.
Default exposure windows are used mainly for protection purposes, to maintain the statistical quality of the results from different intervals as homogeneous as possible. For example suppose that you have a 136 newbin series of which you want to calculate the average power spectrum in intervals of 64 newbins each. Three intervals will be accumulated, two with 64 newbins each and one with 8 newbins. If there were no exposure windows in intervals, the power spectrum the third interval (containing only 8 newbins, i.e. 12.5 % exposed) would be averaged with the power spectra of the first two intervals (both containing 64 newbins, i.e. 100 % exposed).
The side-effects of default exposure windows can be annoying sometimes. For example, when intensity windows in bins or newbins have been specified, and it is difficult to evaluate a priori which fraction of bins and newbins will be accepted, one might end up with many newbins and/or intervals rejected by default exposure windows. Also when specifying time or phase windows, the default windows might need to be reset depending on what fraction of bins and newbins will actually be accepted.
If you do not want any exposure windows you can create (with xronwin) and use a window file containing no exposure windows.