Spectrum of the OFFSET field used for the background estimation, after subtraction of the NXB and the point sources. The XIS BI (Black) and FI (Red) spectra are fitted with CXB + Galactic components (LHB, MWH, and HF) (apec+ phabs(apec+powerlaw+apec)). The CXB spectrum is shown with a black curve, and the LHB, MWH, and HF components are indicated with green, blue and gray curves, respectively.