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## Creating an RMF

In general the spectra generated from the pipeline products are adequate for most analysis. This means that custom RMFs are not needed and the off-the-shelf RMFs provided in the Chandra CALDB are suitable for spectral analysis. Custom RMFs should be generated for spectra extracted with non-standard extraction regions, with non-standard gridding, when analyzing higher order spectra (order > 3) or if the observation is more than 90 off-axis.

Mkgrmf program generates an OGIP style RMF appropriate for spectral analysis of grating observations. The RMF is a representation of how the incident source photons are redistributed onto the detector, thus the grating RMF contains the HRMA + grating line spread function (LSF) vs energy for a given detector and grating combination.

mkgrmf calculates the RMF on user defined set of grid points, e.g. wavelength channel. To create a third order grating rmf

            mkgrmf grating_arm="HEG" order=3 outfile="heg3.rmf" \
            obsfile="./acis_f1235_000N002_pha2.fits" \
            wvgrid_arf="compute"\
            wvgrid_chan="compute"\
            src_id=1

Computes a third order RMF for the HEG, writes the output to heg3.rmf and uses the default grids for the rmf. Note setting the parameter wvgrid_arf to "1.0:21.48:#8192" is equivalent to setting it to compute. In addition to creating rmfs using the standard grid a custom grid can be generated

            mkgrmf grating_arm="LEG" order=1 outfile="leg1.rmf" \
            obsfile="./hrcf00058N002_pha2.fits" \
            wvgrid_arf="1.0:205.8:0.01"\
            wvgrid_chan="1.0:205.8:0.01"

Computes a first order RMF for the LEG, writes the output to leg1.rmf and uses non-standard grids for the rmf.