Cross Spectral Calibration of Suzaku, XMM-Newton, and Chandra with PKS 2155-304 as an Activity of IACHEC

We report on comparisons of the energy responses of the Suzaku XIS, the Chandra HRC and ACIS with the LETG, and the XMM-Newton MOS and pn using simultaneous data of the BL Lac object PKS 2155-304 taken in 2005, 2006, and 2008. From power-law fits to individual spectra, we have found that the photon index agrees among all instruments within simeq 0.1, and that the resultant hydrogen column density values of the Chandra and XMM-Newton instruments differ from the value for PKS 2155-304 only by lesssim 1 ×10 ²⁰cm^-2, while that of Suzaku bears a larger systematic error of 4×10²⁰cm^-2, at most. We have carried out flux cross-calibration in seven small segments of energy bands between 0.5 keV and 10 keV. In the bands above 2 keV, the Suzaku fluxes are larger than those of XMM-Newton by simeq;20%, simeq10%, and lesssim 5% in 2005, 2006, and 2008, respectively, although the 20% difference in 2005 is still preliminary. The fluxes of the LETG/HRC in 2006 coincide with those of Suzaku below 2 keV. The fluxes of the LETG/ACIS are compared with those of Suzaku and XMM-Newton with the 2008 data, and are systematically larger than those of Suzaku and XMM-Newton by 10%. These results are in general consistent with those presented in one of the precedent papers from International Astronomical Consortium for High Energy Calibration (IACHEC) using G21.5-0.9.