The energy grid of the ARF and RMF files must be the same for use in XSpec.

Sherpa allows you to use different energy grids for your ARF and RMF files, but XSpec does not. Note that XSpec will still run if the grids do not match, but it issues a warning and sets all values in the ARF to unity (1).

1. Create the RMF first

   Since mkacisrmf can change the requested grid to match the calibration data, create the RMF first and then use it to define the energy grid when creating the ARF. This will work for both mkarf and mkwarf:

   unix% pset mkarf \
         engrid="grid(sources_ciao.wrmf[cols ENERG_LO,ENERG_HI])"
   
   or
   
   unix% pset mkwarf \
         egridspec="grid(sources_ciao.wrmf[cols ENERG_LO,ENERG_HI])"
   

2. Match an existing ARF

   If the specextract, psextract or acisspec scripts were used, you already have an ARF file for the data. Rather than remake both the RMF and ARF, get the grid information from the history in the ARF file:

   unix% dmhistory acis_src1.warf tool=all
   # dmhistory (CIAO 4.1): WARNING: Found "pixlib" library parameters
   
   # dmhistory (CIAO 4.1): WARNING: Found "ardlib" library parameters
   
   mkwarf infile="acis_src1.[WMAP]" outfile="acis_src1.warf" weightfile="acis_src1.wfef" 
   spectrumfile="" egridspec="0.3:9.5:0.01" threshold="0" feffile="CALDB" 
   mskfile="" mirror="HRMA" detsubsysmod="" ardlibpar="ardlib" geompar="geom" 
   clobber="no" verbose="2"  
   

   Your file may have been created with mkarf instead of mkwarf; the dmhistory tool=all will show the tool used in either case.

   Use the egridspec value (or engrid in the mkarf case) as input for the energy parameter in mkacisrmf:

   unix% pset mkacisrmf energy="0.3:9.5:0.01"
   

The mkacisrmf analysis thread has information on creating the RMF file.