Create and Display a Light Curve

The background is assessed through examination of the light curve. We will extract a region, CCD9, that is most susceptible to proton events and generally records the least source events due to its location close to the optical axis. Also, to avoid confusing solar flares for source variability, a region filter that that removes the source from the final event list should be used. The region filters are kept in the source file product P*SRCLI_*.FIT. (For our example data, this would be P0134520301R1S001SRCLI_0000.FIT).

To create a light curve using the heraXmmselect GUI:

1)

Enter the filtering criteria in the ``Selection expression'' box at the top of the xmmselect GUI:
(CCDNR==9)&&(REGION(P0134520301R1S001SRCLI_0000.FIT:RGS1_BACKGROUND,BETA_CORR,XDSP_CORR))

2)

Check the diamond to the left of the time entry.

3)

Click on the ``OGIP Rate Curve'' button near the bottom of the page. This brings up the evselect GUI (Figure 5.3).

4)

In the ``Lightcurve'' tab, confirm that the withrateset box is checked. Change the timebinsize to a reasonable amount, e.g. 10 or 100 s, and change the default output file name in the rateset box to something appropriate, in this case, r1_ltcrv.fits.

5)

Click on the ``Run'' button at the lower left corner of the evselect GUI.

The resultant light curve is displayed automatically using POWplot (see Figure 8.2).

To create a light curve using the Command Window, type:

evselect table=rgs1.fits withrateset=yes rateset=r1_ltcrv.fits
$$ maketimecolumn=yes timebinsize=100 makeratecolumn=yes
$$ expression=
$$ '(CCDNR==9)&&(REGION(P0134520301R1S001SRCLI_0000.FIT:RGS1_BACKGROUND,BETA_CORR,XDSP_CORR))'

where

table - input event table
withrateset - make a light curve
rateset - name of output light curve file
maketimecolumn - control to create a time column
timebinsize - time binning (seconds)
makeratecolumn - control to create a count rate column, otherwise a count column will be created

expression - filtering criteria

The output file r1_ltcrv.fits can be viewed with fv. The light curve is shown in Figure 8.2.

Figure 8.2: Background event rate from the RGS1 CCD9 chip. The flares are solar events. The time units are elapsed mission time.