The arf.fits file is saved as defined by the OGIP Calibration Memo CAL/GEN/92-002.

It contains 3 columns called: ENERG_LO[kev], ENERG_HI[kev] and SPECRESP[cm2]. 

The ARF energy range is from 5 keV to 85 keV in steps of 0.5 keV. Included in the effective areas are:

Be window attenuation, t = 50 um
MLI attenuation
