The SMC SNR 1E0102.2-7219 as a calibration standard for X-ray astronomy in the 0.3-2.5 keV bandpass

The flight calibration of the spectral response of CCD instruments below 1.5 keV is difficult in general because of the lack of strong lines in the on-board calibration sources typically available. We have been using 1E 0102.2-7219 the brightest supernova remnant in the Small Magellanic Cloud, to evaluate the response models of the ACIS CCDs on the Chandra X-ray Observatory (CXO), the EPIC CCDs on the XMM-Newton Observatory, the XIS CCDs on the Svzaku Observatory, and the XRT CCD on the Swift Observatory. E0102 has strong lines of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the spectrum. The spectrum of E0102 has been well characterized using high-resolution grating instruments, namely the XMM-Newton RGS and the CXO HETC, through which a consistent spectral model has been developed that can then be used to fit the lower-resolution CCD spectra. Fits with this model are sensitive to any problems with the gain calibration and the spectral redistribution model of the CCD instruments. We have also used the measured intensities of the lines to investigate the consistency of the effective area models for the various instruments around the bright 0 (similar to 570 eV and similar to 654 eV) and Ne (similar to 910 eV and similar to 1022 eV) lines. We find that the measured fluxes of the O VII triplet, the O VIII Ly alpha line, the Ne IX triplet, and the Ne X Ly alpha line generally agree to within +/- 10% for all instruments, with 28 of our 32 fitted normalizations within +/- 10% of the RGS-determined value. The maximum discrepancies, computed as the percentage difference between the lowest and highest normalization for any instrument pair, are 23% for the O VII triplet, 24% for the O VIII Ly alpha line, 13% for the Ne IX triplet, and 19% for the Ne X Ly alpha line. If only the CXO and XMM are compared, the maximum discrepancies are 22% for the O VII triplet, 16% for the O VIII Ly alpha line, 4% for the Ne IX triplet, and 12% for the Ne X Ly alpha line.