gammapy dataset representation of NuSTAR A for night 1 is shown here. NuSTAR B for this observation and NuSTAR A/B for night 2 are similar. From top-left to bottom-right: (a) estimated distribution of background events from the OFF rectangular region of Fig. 3 and the ON event distribution from the signal extraction region. (b) Estimated distribution of background events from nuskybgd. ON event distribution identical to the previous case. (c) NuSTAR A exposure (effective area × livetime) as a function of true energy. (d) NuSTAR A energy dispersion matrix.