A versatile facility for the calibration of X-ray polarimeters with polarized and unpolarized controlled beams

TL;DR

This paper presents a versatile calibration facility for X-ray polarimeters, capable of producing polarized and unpolarized beams at multiple energies, enabling comprehensive testing of imaging devices and systematic effect analysis.

Contribution

The authors developed a flexible, automated calibration setup with tunable polarization and energy, improving the precision and scope of X-ray polarimeter calibration.

Findings

Effective production of polarized photons at multiple energies.

Automated, high-precision beam direction control.

Capability to map detector response and systematic effects.

Abstract

We devised and built a versatile facility for the calibration of the next generation X-ray polarimeters with unpolarized and polarized radiation. The former is produced at 5.9 keV by means of a Fe55 radioactive source or by X-ray tubes, while the latter is obtained by Bragg diffraction at nearly 45 degrees. Crystals tuned with the emission lines of X-ray tubes with molybdenum, rhodium, calcium and titanium anodes are employed for the efficient production of highly polarized photons at 2.29, 2.69, 3.69 and 4.51 keV respectively. Moreover the continuum emission is exploited for the production of polarized photons at 1.65 keV and 2.04 keV and at energies corresponding to the higher orders of diffraction. The photons are collimated by means of interchangeable capillary plates and diaphragms, allowing a trade-off between collimation and high fluxes. The direction of the beam is accurately arranged by means of high precision motorized stages, controlled via computer so that long and automatic measurements can be done. Selecting the direction of polarization and the incidence point we can map the response of imaging devices to both polarized and unpolarized radiation. Changing the inclination of the beam we can study the systematic effects due to the focusing of grazing incidence optics and the feasibility of instruments with large field of view.