WINGSPAN displays the burst spectrum and history in a work window ( Burst History/Spectrum). The Burst History/Spectrum window selection buttons are shown in Figure 10.
Figure 10:
Burst History/Spectrum Selection Buttons
You can toggle between the History and Spectrum windows using the button Toggle Work Window. Using these two windows and their associated commands, you can select subsets of the data for display and further processing, e.g., spectral model fitting. The energy range you select in the Burst Spectrum window is displayed in the Burst History window, similarly the sum of the ``observed'' time intervals selected in the Burst History window is displayed in the Burst Spectrum window. The Burst History window is also used to choose background intervals which are used to create the background model. You can change the binning of the data in each of these windows. The data selections and binning combinations you make in the Burst Spectrum and Burst History windows determine the data displayed in the Spectral History window and the data available for fitting via the Fit Spectrum / MFIT option (see §2.3). The details of the selection and combination options are covered in the following sections.
To change the energy binning of your data, select the Burst Spectrum entry from the main menu. You may use the button or click directly in the window. A work window will appear that contains the options shown in Figure 10. As you select each of these buttons, consult the STATUS area for instructions and for the current state of the program. The EXIT command returns you to the main menu.
When you select the Default Lookups entry, WINGSPAN will replace the current binning of your data with the program's default binning. When you first invoke WINGSPAN, the default binning is the binning at which your data is stored in the FITS file, but you may change the default binning by selecting the Save or Read entries under the Lookup Filename command (see §2.1.5).
When you select the Full Resolution entry, WINGSPAN will display your data with the binning at which it is stored in the FITS file. If you have not changed the default binning with Save or Read under the Lookup Filename command, the Full Resolution and Default Lookups commands are identical.
To display only a portion of your data's energy channels or time bins on a Spectral History plot, use the Select Source Intervals command. When you exit the Burst Spectrum command, the Burst History window will also be updated to display count rates integrated over the selected energy range. Conversely, changes made in selections in the Burst History option will be reflected in the Burst Spectrum window upon exiting.
After you choose Select Source Intervals, WINGSPAN will wait for you to select a range of bins. Select the first bin in the range you wish to combine by moving the cursor over the bin in the plot and pressing the left mouse button. Select the last bin in the same way. Numbers in the lower left-hand corner of the plot track the position of the mouse cursor, which can be used if a particular value is to be selected. For precise selection, move the cursor below the bottom axis of the plot. The message in the lower left-hand corner of the plot will change to ``Numerical Entry''. If you click the mouse button in this area of the plot, WINGSPAN will prompt you to type two numbers to bound the selection interval. The selected interval will be the smallest one that encompasses the bin(s) containing the numbers entered. WINGSPAN will respond to the selection by displaying the actual values of the edges of the selected interval. If you make a mistake and want to start over, move the cursor past the right-hand vertical axis of the plot, until the message in the lower left-hand corner of the plot reads ``RESET'', and press the left mouse button. The plot will revert to the default selection (the entire range), and you can start over.
After you select the two bins, WINGSPAN will move the vertical lines on the plot so that they bound the range of bins you have selected. If you are working in the Burst Spectrum window, the rates in the selected channels are averaged to produce the history displayed in the Burst History window. You may continue to select ranges of bins by clicking on two bins on the spectrum plot, setting up additional non-overlapping (and possibly discontiguous) selections. This may be useful in the Stacked Histories spectral history type, when you want to compare the rates at one energy range with rates at other energies. You exit the command by selecting a point on the plot to the left of the left, vertical axis, so that the message in the lower left-hand corner of the plot reads ``EXIT''.
Keep in mind that any discontiguous selection of bins can be made, and that selections outside of the range of a zoomed view might exist if you made them previously. To return to the default selection, which is the entire range, select a point on the plot to the right of the right vertical axis. Any combined Time Bin on the Burst History plot is available for fitting; however, only the selected Source Intervals are available for Batch Fitting and for display in the Spectral History Window.
Too many selected time bins will be confusing in the Stacked Spectra mode of the Spectral History command, so if you intend to use this option the selection should be limited to less than about 12 combined time bins, depending upon the resolution of your terminal's display. In any case, WINGSPAN will refuse to display more than 25 plots in the Spectral History window. You may reduce the number of combined time bins by selecting a smaller observed time interval or by combining some time bins. You will frequently want to combine time bins via the Combine or, better, the Bin for Significance commands to generate spectra with better statistics. As described below, the Bin for Significance command combines time bins until a desired signal to noise ratio is attained in the background-subtracted data. These combined time intervals should generate more consistent results when a given spectral model is applied to each in turn, via the batch fitting procedure, described below.
The Select Background Intervals command is used to create the background model, which is used to create background-subtracted source spectra. Select Background Intervals is valid only in the Burst History window. Each selected range of bins in the background intervals will be displayed as a dotted histogram. The default, which is no background intervals, can be returned to at any time by selecting a point on the plot to the right of the right vertical axis. After the selection is complete, or when you desire to return to the main menu, say to zoom in or out to better select other portions of the background, select a point on the plot to the left of the left vertical axis.
You will be asked to choose the order of the background model to be used for
the fit, or you can cancel the procedure. The coefficients of the background
model are computed at this time, after which the background model, integrated
over energy, will be displayed as a line plotted over the time histogram. This
line will appear dotted where it has been interpolated or extrapolated beyond
the time bins selected for the background model fit, and, in particular, will
be interpolated through the burst interval. This allows the user to visually
estimate the amount of signal above background for the source spectra, as well
as visually evaluate the appropriateness of the background model. While a
continuous background model is shown on the plot, background subtraction is
done by averaging the background model over the accumulation time of each
source data interval. You will also be given the choice of viewing a plot of
reduced 
for the background model versus energy channel over the
selected energy range. You can change the order of the background model without
changing the background intervals selection by again choosing the
Select Background Intervals subcommand and immediately EXITing.
The background model is created, for each channel, by fitting a polynomial of
the selected order to the data. The average of the polynomial over each time
bin is calculated and compared to the data, and the polynomial coefficients are
optimized so as to minimize . For all except the strongest bursts at
low energies, selection of the background model needs to be done with care.
Lower orders probably lead to a more stable and robust background model, but
models of low order frequently cannot reproduce the observed background time
variations. You must balance systematic errors in the background model caused
by choosing more data than can be fit with a polynomial versus the large
statistical error bars caused by creating the background model using a small
interval of data. If your source time intervals are an extrapolation,
rather than an interpolation, of the background model, it would be wise to
select a low order.
The Combine entry permits you to combine a sequence of bins into a single bin. When you select Combine, a pull-down menu appears asking what type of binning is desired. Combine into 1 Bin means that all the bins selected by the mouse will be joined into one bin; whereas Group by Twos means that every two bins in the range selected by the mouse will be combined into one bin. Group by ... will bring up a choice of numbers of bins to combine into one bin, and works similarly as the Group by Twos command. WINGSPAN will wait for you to mark two bins from the spectrum plot in the manner described previously, in the Select... commands. After you select the last bin, WINGSPAN will redraw the spectrum plot with the selected binning. The program will then wait for you to combine another range of bins. ``RESET'' works as described above, changing the binning back to the default resolution, as does ``Numerical Entry'', for typing the bounds of the region to be combined. Combine Selections will combine all selected source intervals into a single bin (per selected interval). To exit, move the cursor to a point on the plot to the left of the left, vertical axis, until the message in the lower left-hand corner reads ``EXIT'', and press the mouse button.
The subcommand menu under Combine has two additional choices unique to the Burst Spectrum plot: you can choose to combine a range of bins to either half of the detector energy resolution, or to the full resolution. This is useful for spectroscopy data types which have energy bin widths narrower than the detector response. Binning the data close to the resolution of the detector offers a good indication of which features are significant. Note that these selections are only available if you select the Burst Spectrum window from the main menu. If you select the Burst History window from the main menu, and then toggle to the Spectrum window, these two choices will not be available.
You may want to bin your data so that each data point has roughly the same level of statistical significance above background. After a background model has been computed, the Bin for significance command lets you bin your data so that the rate in each bin has an error bar smaller than a size you specify. When you select Bin for Significance, WINGSPAN will prompt for you to enter a desired Signal to Noise Ratio (SNR) for the background-subtracted data. WINGSPAN will attempt to reduce the size of your data's error bars by combining bins. The choice of SNR will involve some trial and error. For the Burst History window, SNRs are calculated based upon the total number of energy bins selected in the Burst Spectrum window, and vice versa. Thus, if only one energy bin has been selected (spanning 5 keV), you would supply a correspondingly smaller SNR than if the entire energy range (roughly 2 MeV) were selected, in order to obtain an equivalent time binning. As a rough guide for the BATSE HER data, if most of the energy range is selected (the overflow channels at the high end, as well as channels below the LLD, should usually be excluded for spectroscopic analyses), a number above 15 will usually produce spectra that have enough significance above background to be fit reliably.
Once you have combined a sequence of energy bins, you may wish to undo the operation and display your data at its full resolution again. The Refine command allows you to reverse the effect of the Combine command. Select Refine, and WINGSPAN will wait for you to select a bin from the spectrum plot. When you select a bin, WINGSPAN will redraw the plot with the data within the selected bin displayed at your file's full resolution. After redrawing the plot, WINGSPAN will wait for you to refine another bin. To exit the Refine command, select a point to the left of the left, vertical axis.
The Refine by Half command is a less drastic version of Refine. It divides a large, combined bin into two smaller bins, each roughly half the width of the original.
You can make a hard copy of the plot displayed in the work window at any time by selecting the Create Hardcopy command. The output is send to the device pointed to by WING_PRINTER, which is defined in the wing.pro file.
The Zoom pulldown menu offers several options to change the intervals of data that are displayed. These options are described in the following sections.
When the resolution of your data is fine, you may have difficulty selecting a single bin with the cursor in the manner described under the commands Select and Combine. To ease the selection of bins, you may reduce the number of bins displayed with the Zoom command. Select Zoom and WINGSPAN will wait for you to select two points on the plot with the mouse. These two points should be the diagonal corners of a box which includes all the data you wish to display. To aid selection, the lower left corner of the plot will display the current cursor position. In addition, after the first point is selected, a dotted box will follow the cursor, as an indication of the region of the plot which will be expanded. Do not hold down the mouse button as you draw the box. Click once to select a corner, and release the button. Move the mouse to the diagonal corner of the box, and click again. After you select the second point, WINGSPAN will redraw the plot. If you wish to exit the command without redrawing, select a point on the plot to the left of the left, vertical axis. You may enter selections through the keyboard by clicking in the lower margin (``Numerical Entry'').
If you have previously made selections from the data, you can immediately jump to a view of the entire selection by choosing the Zoom In: Selection command. This is the best method for switching between an overview of the entire dataset (see Zoom out: Full Range below) and your selected data. If you have not specifically made any selections, the default selection is the entire dataset, so for this case, the command is identical to the Zoom out: Full Range command. You can also use this command to see if there are any selection regions outside the current view of the data. In the Burst History plot, the command works on the selected source intervals, not on the selected background intervals.
When you have zoomed in on your data and you wish to display all of the data again, select the Zoom out: Full Range entry. The Zoom Out: By Twos command doubles the size of the viewing rectangle in both axes each time it is chosen, so that the user can `step back' gradually from a close-up view. The range doubling continues independently in each axis until the maximum range of the data for that axis is reached, after which re-selection of the command has no effect.
Select this button to expand the currently displayed plot to the full screen size.
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