Design of conical Wolter-I geometry with sectioned secondary mirrors for x-ray telescopes

Abstract

Conical Wolter-I geometry is employed for many x-ray telescopes to lower their cost and fabrication difficulty at the expense of angular resolution. Owing to the conic error, the angular resolution of conical Wolter-I geometry is much worse than that of Wolter-I geometry, especially for the telescopes with large diameter. We optimized the conical Wolter-I geometry to significantly improve the angular resolution. We designed a conical Wolter-I geometry with sectioned secondary mirrors. Based on the normal conical Wolter-I geometry, we divided the secondary mirror into two equal sections along the optical axis. In this case, the collecting area was reduced by 5% because of the interval between the two sections. Meanwhile, the conic error was reduced by about 50%, indicating a great improvement in angular resolution. Regarding our improvement in the thermal slumping technique, it is feasible to fabricate sectioned mirrors, thus improving the angular resolution by 50% at the cost of a 5%-reduction in collecting area. In addition, a hybrid geometry, comprising the sectioned and nonsectioned geometries, is proposed as an alternative for x-ray telescopes with a large amount of nested shells, to obtain both a large collecting area and decent angular resolution.

Development of imaging x-ray telescopes at Tongji University

“…In addition, we proposed two optimized geometries to improve the IXT performance, which are a hybrid configuration and a sectioned configuration. 20,21 The hybrid configuration uses one conical surface and one quadratic surface, while the sectioned configuration is a conical Wolter-I configuration with sectioned secondary mirrors.…”

Calibration of X-ray telescope prototypes at PANTER

“…To reduce the difficulty and cost of mirror fabrication, the conical Wolter-I configuration was put forward in the 1980s (Petre et al 1985;Serlemitsos 1988). In recent years, two optimization solutions were proposed by the Institute of Precision Optical Engineering (IPOE), which are a hybrid and a sectioned configuration (Chen et al 2016;Liao et al 2019). The hybrid configuration consists of one conical surface and one quadratic surface, while the sectioned configuration is based on a conical Wolter-I configuration with sectioned secondary mirrors.…”