NuSTAR low energy effective area correction due to thermal blanket tear

Understand

A rip in the MLI at the exit aperture of OMA, the NuSTAR optic aligned with detector focal plane module FPMA, has resulted in an increased photon flux through OMA that has manifested itself as a low energy excess.

• Overall, the MLI coverage has decreased by 10%, but there is an additional time-varying component, which occasionally causes the opening to increase by up to 20%.
• We address the problem with a calibration update, and in this paper, we describe the attributes of the problem, the implications it has on data analysis, and the solution.