In-orbit monitoring of the imaging x-ray polarimeters on-board IXPE

The imaging x-ray polarimetry explorer (IXPE) was launched on December 9, 2021, from Cape Canaveral into a low-Earth equatorial orbit. The mission, led by NASA in collaboration with the Italian Space Agency (ASI), features three identical telescopes, each with an imaging x-ray photoelectric polarimeter at the focus of an x-ray mirror assembly. Each focal-plane detector includes a set of four calibration sources powered by a 55Fe nuclide to monitor the detector's performance. Of these sources, one produces polarized x-rays at two energies and the remaining three generate unpolarized radiation. Here we present the status of this monitoring program, starting from installation of the flight nuclides before on-ground environmental testing of the observatory through recent on-orbit measurements during science operations.