  We desire a simple comparison of the absolute effective areas of the current
generation of CCD instruments onboard the following observatories: Chandra
ACIS-S3, XMM-Newton (EPIC-MOS and EPIC-pn), Suzaku XIS, and Swift XRT and a
straightforward comparison of the time-dependent response of these instruments
across their respective mission lifetimes. We have been using 1E 0102.2-7219,
the brightest supernova remnant in the Small Magellanic Cloud, to evaluate and
modify the response models of these instruments. 1E 0102.2-7219 has strong
lines of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate
the spectrum. As part of the activities of the International Astronomical
Consortium for High Energy Calibration (IACHEC), we have developed a standard
spectral model for 1E 0102.2-7219. The model is empirical in that it includes
Gaussians for the identified lines, an absorption component in the Galaxy,
another absorption component in the SMC, and two thermal continuum components.
In our fits, the model is highly constrained in that only the normalizations of
the four brightest lines/line complexes (the O vii He$\alpha$ triplet, O viii
Ly$\alpha$ line, the Ne ix He$\alpha$ triplet, and the Ne x Ly$\alpha$ line)
and an overall normalization are allowed to vary. We have examined these
measured line fluxes as a function of time for each instrument after applying
the most recent calibrations that account for the time-dependent response of
each instrument. We perform our effective area comparison with representative,
early mission data when the radiation damage and contamination layers were at a
minimum. We find that the measured fluxes of these lines generally agree to
within +/-10% for all instruments, with 38 of our 48 fitted normalizations
within +/-10% of the IACHEC model value.
