Calibration of the Line Emission Mapper (LEM) Observatory

The Line Emission Mapper (LEM) is a probe-class mission concept to study the distribution of hot, x-ray emitting gas within and surrounding our galaxy, surrounding nearby galaxies, and within and surrounding clusters of galaxies, with high spectral resolution and moderate spatial resolution. LEM is composed of a 1.6m diameter light weight x-ray optic, and an x-ray micro calorimeter spectrometer with ~14,000 spatial resolution elements (pixels) with a spectral resolution of 1 eV at 500 eV (central 1000 pixels) surrounded by a 2 eV resolution extended field-of-view. LEM will have a field of view of 30 arc minutes and a very large grasp of 1.4e6 cm² arc minute² where every spatial resolution element is a fully independent spectrometer. Calibration of the observatory will involve measuring, and measuring the precision of, the observatory parameters such as the effective area, absolute and relative energy scale, energy resolution, and absolute and relative timing. The calibration requirements for LEM are in most cases more stringent than XRISM/Resolve (and Hitomi/SXS) but less so than Athena/X-IFU, two programs with well-developed calibration plans. Here we present a draft plan for calibrating LEM on the ground and in-flight, which is largely an amalgamation of the XRISM/Hitomi and Athena plans. The LEM calibration team has been heavily involved in the planning and execution of the XRISM/Hitomi calibration plan and the planning of the Athena/X-IFU calibration and bring that experience to defining the LEM plan presented here.