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It was observed early on in the Chandra X-ray Observatory mission that the background rates of the Advanced CCD Imaging Spectrometer (ACIS) were highly variable on both short and long timescales. We present analysis of lightcurves of the high energy (> 15 keV) ACIS background spanning most of the mission lifetime. These high energy events are not produced by astrophysical X-rays, but by the particle background, primarily energetic protons. Temporal characteristics of both the quiescent background and background flares will be discussed as well as correlations with Chandra's orbital position and the solar activity cycle. The strength and frequency of background flares appear cyclic with a quasi-annual period, most likely from the motion of Chandra's orbit through the geomagnetic environment., 7 pages, 5 figures. To appear in ``The High Energy Universe at Sharp Focus'' (St. Paul, Minnesota 2001), eds Schlegel and Vrtilek (ASP Conference Series)

The flight calibration of the spectral response of the Advanced CCD Imaging Spectrometer (ACIS) below 1.5 keV is difficult because of the lack of strong lines in the calibration source on-board the Chandra X-ray Observatory. We have been using 1E0102.2-7219 (the brightest supernova remnant in the SMC) to evaluate the ACIS response matrices, since this remnant has strong lines of O, Ne and Mg below 1.5 keV. The spectrum of 1E0102.2-7219 has been well-characterized using the gratings on Chandra and XMM. We have used the high-resolution spectral data from both gratings instruments to develop a spectral model for the CCD spectra. Fits with this model are sensitive to any problems with the gain calibration and the spectral redistribution model. We have fit the data with the latest response matrix for the S3 device released in August 2001 (available in CALDB 2.7 or higher). We have also applied the charge-transfer inefficiency (CTI) correction software (version 1.37) developed at Penn State to both the Backside-illuminated (BI) and Front-side illuminated (FI) data and fit the data with the associated CTI-corrected response matrices. All fits show a significant improvement in the low energy response with the new matrices. The fits to the FI CCDs demonstrate the utility of the FI CCDs for spectral analysis, in spite of the radiation damage the devices suffered early in the mission., Comment: To appear in ``The High Energy Universe at Sharp Focus'' (St. Paul, Minnesota 2001), eds Schlegel and Vrtilek (ASP Conference Series)