An example of combining contour plots
It is often useful to be able to superimpose contour plots based on multiple steppar or margin commands. This cannot be done within xspec but can be done by combining and editing files produced by xspec and plotting the result using qdp. This page describes an example case of combining the results of steppar commands for the same model but with two different spectra.
The model used was phabs(pow) and the datasets were file1.pha and file2.pha in the ftools/spectral/session directory. The steppar command was:
XSPEC12> steppar 1 8. 12. 25 2 1.2 1.5 25
and the files were written out using
XSPEC12> iplot contour PLT> wenv test1
and
XSPEC12> iplot contour PLT> wenv test2
respectively. This creates files test1.pco, test1.qdp, test2.pco, test2.qdp. The qdp files contain the data and the pco files the commands used to make the contour plots.
Making combined plot requires combining the qdp data files and writing a new pco file. So, copy test1.qdp into a new file:
cp test1.qdp testboth.qdp
Now open an editor and read in testboth.qdp. On the first line replace test1.pco with testboth.pco. Go to the end of the file and insert test2.qdp. The inserted data will start with the lines:
@test2.pco !
Delete these and save the resulting file.
Now copy test1.pco into testboth.pco and open in an editor. If there are lines starting IMAG then delete them because they create the background image which will be confusing if multiple contours are being overplotted. The DG command is used to define data groups. The command
DG 1 1 1 26 26
tells qdp that the first data group is from columns 1 to 26 in rows 1 to 26. This is the data from test1.qdp. Since the data from test2.qdp were appended the second data group is defined using the command
DG 2 27 1 52 26
so this is added to the testboth.pco file. Finally take the CONT commands from test2.pco and add them to testboth.pco changing them all from CONT 1 to CONT 2. The color, style and width of the lines can be changed as necessary to distinguish the two sets of contours. To include a cross at the position of best fit for the second set of contours copy the LAB 1 command from test2.pco and change it to LAB 2. The resulting testboth.pco file will look something like:
LWIDTH 2. COL OFF 1..26 DG 1 1 1 26 26 LIne ON 1 LW 1.0 ON 1 LIne ON 2 LW 1.0 ON 2 CONT 1 LEVEL 82.6023636 84.9123611 89.5123596 CONT 1 COLOR 2 3 4 CONT 1 LSTYL 1 1 1 CONT 1 LWID 1 1 1 XAX LIN 8 0.159999847 YAX LIN 1.20000005 1.19999647E-2 LOC 0 0 1 1 LAB 1 COL 5 LAB 1 POS 9.86781979 1.31636 "+" LAB T Confidence contours: Chi-Squared LAB X Parameter: nH (10\u22\d) LAB Y Parameter: PhoIndex R X1 8 12 R Y1 1.20000005 1.5 DG 2 27 1 52 26 CONT 2 LEVEL 89.659462 91.9694595 96.569458 CONT 2 COLOR 2 3 4 CONT 2 LSTYL 2 2 2 CONT 2 LWID 1 1 1 LAB 2 POS 10.3893003 1.39174998 "+"
Now create the plot using
qdp testboth.qdp