NuSTAR low energy effective area correction due to thermal blanket tear

TL;DR

This paper discusses how a tear in the thermal blanket of the NuSTAR telescope's optics causes increased low-energy photon flux, affecting data calibration, and presents a calibration update to correct this issue.

Contribution

It provides a detailed analysis of the thermal blanket tear's impact on NuSTAR's effective area and offers a calibration correction method.

Findings

10% decrease in MLI coverage

Up to 20% increase in aperture opening

Calibration update improves data accuracy

Abstract

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.