Design and in-orbit calibration of the MXT optics

TL;DR

The paper details the design, in-orbit calibration, and ground testing of the MXT lobster eye X-ray telescope on the SVOM satellite, highlighting its unique wide field of view and calibration procedures.

Contribution

It presents the innovative design and calibration process of the MXT optics, including in-orbit calibration results compared to ground tests.

Findings

In-orbit calibration matches ground-based results.

The lobster eye design provides a 6-degree wide field of view.

The electron diverter's design and limitations are discussed.

Abstract

The Microchannel X-ray Telescope (MXT) is one of four instruments on the Space-based multi-band astronomical Variable Objects Monitor (SVOM) satellite mission, launched on the 22nd June 2024. The MXT is a narrow-field-optimised, lobster eye X-ray focusing telescope, consisting of an array of 25 square MPOs, with a focal length of 1.14 m and working in the energy band 0.2 - 10 keV. The design of the MXT optic (MOP) is optimised to give a 1 degree FoV to match the detector size, but the optic has the unique characteristics of a lobster eye design, with a wide FoV of 6 degree diameter, and a PSF, which is constant over the entire FoV. The MPOs on the Flight Module (FM) MOP have a pore size of 40 um giving the optimum thicknesses across the aperture of 2.4 mm in the centre and 1.2 mm at the edges. Using specific target sources, the in-orbit calibration of the optic is here described, and compared to the extensive on-ground calibration, which was carried out at the PANTER test facility, MPE, Germany. The design and limitations of the electron diverter, situated directly behind the optic, are also discussed.