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Last modified: December 2013

AHELP for CIAO 4.9


Context: tools


Add multiple grating ARF files together, weighting by exposure.


dmarfadd infile outfile [clobber] [verbose]


`dmarfadd' will add several grating ARFs (Auxiliary Response Files) together to create a single output ARF file.

The addresp tool is preferred for combining imaging ARFs and RMFs.

If dmarfadd is used to add imaging ARFs for point sources, it is assumed that the same RMF applies to every ARF. If the RMFs are significantly different, it is advised to NOT combine the ARFs using dmarfadd. It should also be noted that dmarfadd does not produce a sum but an average of the individual ARFS.

In the Chandra case, there is a separate ARF for each detector element (ACIS CCD or HRC MCP). The user can use `dmarfadd' to combine these files to create an ARF that covers the region (spatial or spectral) of interest. Each CCD generally has different good-time intervals (GTI), and hence, a different EXPOSURE. `dmarfadd' weights the ARF by the exposure time and derives a mean EXPOSURE. For grating spectra, where aspect dither causes different chips to overlap the same spectral region, this produces the correct ARF.

In addition to the effective area column (SPECRESP), 'dmarfadd' also averages the 'FRACEXPO' column, which is primarily needed for grating pileup modeling. FRACEXPO is a value between zero and one, which indicates the fractional time that region was exposed by a detector (e.g., it is 1.0 on chip, and drops in chip gaps).

NOTE: (1) The energy grids across the files to be combined must be the same. (2) For grating observations, the keywords, GRATING, (HETG or LETG), TG_PART (which indicates HEG or MEG grating types for HETG), and TG_SCRID must match across the files. (3) The keyword EXPOSURE must exist in all input files. (4) For gratings, TG_M must match in absolute value (that is, orders -1 and +1 may be added, but not 1 and 2). For imaging-mode (GRATING='NONE'), the grating keywords are ignored.

Example 1

ls acis*MEG_-1.fits > data.lis
dmarfadd @data.lis acis_MEG_-1_garf.fits

Make a list of grating ARF components for MEG order -1 in file data.lis. Open the file "data.lis" and combine the files listed in the file to the output file, acis_MEG_-1.fits

Example 2

dmarfadd "m1_arf.fits,m2_arf.fits" output.fits

This will combine the files m1_arf.fits and m2_arf.fits and place the results in output.fits.


name type ftype def min max reqd stacks
infile file input       yes yes
outfile file output       yes  
clobber boolean   no        
verbose integer   0 0 5    

Detailed Parameter Descriptions

Parameter=infile (file required filetype=input default= stacks=yes)

Input list of files.

The input list of files to be combined into one output file.

Parameter=outfile (file required filetype=output default=)

Output dataset name

This is the resultant combined ARF. All input files are combined into this output.

Parameter=clobber (boolean default=no)

If "yes", then overwrite any existing output file. If a file exists and clobber is set to "no", the tool will exit with an error message.

Parameter=verbose (integer default=0 min=0 max=5)

Control the amount of diagnostic output to file from none (0) to a maximum (5).


The TG_M keyword is incorrect in the output file with single input file

The TG_M keyword in the output ARF is incorrect when using dmarfadd with a single input file, ie when simply copying the ARF.

The value written to the header is random; but often shows up as 0 regardless of the input value.

See Also

acis_bkgrnd_lookup, acis_fef_lookup, acis_set_ardlib, addresp, aprates, asphist, combine_grating_spectra, combine_spectra, dither_region, dmextract, eff2evt, fullgarf, hrc_bkgrnd_lookup, make_instmap_weights, mean_energy_map, mkacisrmf, mkarf, mkexpmap, mkgarf, mkgrmf, mkinstmap, mkpsfmap, mkrmf, mkwarf, psextract, psf_project_ray, readout_bkg, rmfimg, sky2tdet, specextract

Last modified: December 2013
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