Even when the Sun is quiet, there are some counts in the four energy bands due to X-rays from the calibration sources, as well as e.g., cosmic X-ray radiation. For a better HXT data analysis, we recommend you carefully subtract non-flare background from flare data you are going to analyze. The typical background (BGD) count rates in the four energy bands are:
One must be careful since the above BGD count rates have an orbital dependence; for example, the NaI scintillators are activated during SAA passages and there are some excess counts in the four bands even after exit from SAA. The most suitable way for background subtraction that we recommend at present is to use data just before or after the flare as BGD.
Background subtraction plays an important role in image synthesis as well as spectral analysis with HXT. This is especially true if you are going to analyze not-so-intense flares. Even for intense flares, image synthesis with inappropriate background subtraction will provide you with images with spurious sources scattered around in the image synthesis FOV.