xmmselect table=PN.evt &
The xmmselect call pops-up a window similar to that shown in Fig.1.
Fig.1: The main xmmselect
window
In this window, we identify:
- a data screening widget (top)
- a data column panel (middle)
- the buttons 1D region and 2D region, which allow to translate selection expression defined in a grace or ds9 window, respectively, into proper selectlib expressions
- "action" buttons (bottom)
- writing the following selection expression in the data screening widget: '#XMMEA_EP && (PI>10000) && (PATTERN==0)' (cf. Fig.1)
- clicking on the radio button close to the TIME column in the data column panel
- clicking on "OGIP rate curve"
This will pop-up another window: the evselect parameter user interface (see Fig.2).
Fig.2: The main evselect
window
On this multi-panel window, one should at least:
- click on the Lightcurve menu (and this leads you to the sub-panel shown in Fig.3)
- define the output file name in the rateset widget (e.g.:ratePN.fits)
- define the time bin size (in seconds) in the timebinsize widget
- click Run
Fig.3: The Lightcurve panel in the evselect window
As customary for SAS task, each widget, button or menu in the evselect window corresponds to a task parameter. The whole list of available evselect parameters, with their description, is available at the evselect task description.
Once Run is clicked, dsplot is silently run on the created light curve, and the corresponding grace window appears (see Fig.4)
- go to the item Edit/Region/Define
- define region type (e.g.: in Horiz. Range)
- click Define
- click oncewith the right mouse on the grace window to define the starting time of the first interval, and once to define the end time.
- repeat this as many times as needed. Just be aware that the counter Define region: needs to be updated, if you want to define 7.0.0 regions (i.e., not to overwrite the old ones)
Fig.4: A grace
window, displaying a light curve, and one interval created as explained
in text
Be aware that grace allows you to define several different types of intervals. Among the normally most useful: Above/below line, in Vert. range,Out of Horiz/Vert. range, Left/Right of line
When you are happy with your definition, click the button 1D region in the xmmselect window. The selection region will be automatically transferred into the data selection widget of the xmmselect window, and properly translated into a selectlib expression
- clicking the square checkbox besides X and Y in the data column xmmselect panel
- click on Image
- go the the Image sub-panel in the evselect window (see Fig.5)
- change at least the file name in the imageset window (e.g. to PNimage.fits)
- [remember to remove the selection expression you used to generate the background light curve from the Selection expression widget]
- click Run
Fig.5: The Image panel in the evselect window
xmmselect will automatically launch a ds9 window on the created image
Fig.6: Spectrum extraction region optimization window in especget
- Use optimized region: allows the user to extract the source+background spectrum from a circular region, which maximizes the signal-to-noise ratio. The properties of this optimal region are displayed in the window
- Use initial region: allows the user to extract the source+background spectrum from the region initially chosen
- Start over: allows the user to start the whole process again, from the definition of spectral extraction regions in the field-of-view image (step 6. above)
Fig.7: Main especget
window
- stem_srcspec.ds: source+background spectrum
- stem_bckspec.ds: background spectrum
- stem_srcspec.rmf: redistribution matrix
- stem_srcspec.arf: effective area vector
FTOOL: grppha: PHA filename: mypn_src.ds
output filename: PNsource_spectrum.grp
group min 25 ! as an example
exit
For bright sources and sources with narrow lines it might be better to extract two spectra and corresponding backgrounds, response and ancillary files: one set for single pixel events (PATTERN==0) and another set for doubles (PATTERN IN [1:4]).
Fitting these two spectra simultaneously will show if there are any problems with pile-up (see also SAS task epatplot) and - as the energy resolution for singles is slightly better than the one for doubles - will show the line features at highest energy resolution in the single events spectra.
However, in case of TIMING mode observations (where the rate of single to double events depends on the source position) one should always create and fit a spectrum of the combined single and double events.